ClassCastException when upgrading to Kotlin 1.4

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When executing ./gradlew run in our project on this commit and pressing "Neues Spiel starten" in the GUI, the following error occurs. The commit after that downgrades Kotlin, and the error vanishes.

Oct 28, 2020 1:55:30 P.M. tornadofx.DefaultErrorHandler uncaughtException
SEVERE: Uncaught error
java.lang.ClassCastException: class tornadofx.BindingAwareSimpleStringProperty cannot be cast to class javafx.beans.property.ObjectProperty (tornadofx.BindingAwareSimpleStringProperty is in unnamed module of loader 'app'; javafx.beans.property.ObjectProperty is in module javafx.base of loader 'app')
	at sc.gui.model.TeamSettingsModel.<init>(GameCreationModel.kt:48)
	at sc.gui.controller.GameCreationController.<init>(GameCreationController.kt:16)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500)
	at java.base/java.lang.reflect.ReflectAccess.newInstance(ReflectAccess.java:124)
	at java.base/jdk.internal.reflect.ReflectionFactory.newInstance(ReflectionFactory.java:346)
	at java.base/java.lang.Class.newInstance(Class.java:604)
	at tornadofx.FXKt.find(FX.kt:437)
	at sc.gui.view.GameCreationView$$special$$inlined$inject$2.getValue(Component.kt:1364)
	at sc.gui.view.GameCreationView$$special$$inlined$inject$2.getValue(Component.kt:212)
	at sc.gui.view.GameCreationView.getController(GameCreationView.kt)
	at sc.gui.view.GameCreationView$root$1$2$1$1.invoke(GameCreationView.kt:25)
	at sc.gui.view.GameCreationView$root$1$2$1$1.invoke(GameCreationView.kt:14)
	at tornadofx.LayoutsKt.vbox(Layouts.kt:433)
	at tornadofx.LayoutsKt.vbox$default(Layouts.kt:144)
	at sc.gui.view.GameCreationView$root$1$2$1.invoke(GameCreationView.kt:24)
	at sc.gui.view.GameCreationView$root$1$2$1.invoke(GameCreationView.kt:14)
	at tornadofx.LayoutsKt.hbox(Layouts.kt:429)
	at tornadofx.LayoutsKt.hbox$default(Layouts.kt:137)
	at sc.gui.view.GameCreationView$root$1$2.invoke(GameCreationView.kt:23)
	at sc.gui.view.GameCreationView$root$1$2.invoke(GameCreationView.kt:14)
	at tornadofx.FormsKt.form(Forms.kt:342)
	at sc.gui.view.GameCreationView$root$1.invoke(GameCreationView.kt:22)
	at sc.gui.view.GameCreationView$root$1.invoke(GameCreationView.kt:14)
	at tornadofx.LayoutsKt.borderpane(Layouts.kt:465)
	at sc.gui.view.GameCreationView.<init>(GameCreationView.kt:18)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500)
	at java.base/java.lang.reflect.ReflectAccess.newInstance(ReflectAccess.java:124)
	at java.base/jdk.internal.reflect.ReflectionFactory.newInstance(ReflectionFactory.java:346)
	at java.base/java.lang.Class.newInstance(Class.java:604)
	at tornadofx.FXKt.find(FX.kt:437)
	at tornadofx.FXKt.find$default(FX.kt:426)
	at tornadofx.UIComponent.replaceWith(Component.kt:1259)
	at tornadofx.UIComponent.replaceWith$default(Component.kt:1258)
	at sc.gui.controller.AppController.changeViewTo(AppController.kt:16)
	at sc.gui.view.StartView$root$1$1$2$1$1.handle(StartView.kt:29)
	at sc.gui.view.StartView$root$1$1$2$1$1.handle(StartView.kt:9)
	at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
	at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
	at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
	at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
	at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
	at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
	at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
	at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
	at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
	at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
	at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
	at javafx.graphics/javafx.scene.Scene$ClickGenerator.postProcess(Scene.java:3569)
	at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3871)
	at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1849)
	at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2590)
	at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:409)
	at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:299)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
	at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:447)
	at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:412)
	at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:446)
	at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556)
	at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942)
	at javafx.graphics/com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
	at javafx.graphics/com.sun.glass.ui.gtk.GtkApplication.lambda$runLoop$11(GtkApplication.java:277)
	at java.base/java.lang.Thread.run(Thread.java:832)

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Worked around it by explicitly declaring the type of the binding result as Property after seeing edvin/tornadofx#1285