Arabic shadda and out of position when it comes between ain and lam, and it prevents the ain and lam from connecting

[MatthewWilliamsCMH]

Using Cairo variable, in this sequence, "فَعَّل," the medial ain will not connect to the lam. The shade (0651 + 0643) intervenes and sets in the wrong position.

To Reproduce
In InDesign (perhaps other programs as well), key or copy/paste the sequence with Cairo variable loaded and applied. Then Unload Cairo variable and load Cairo Regular static to see what the corrected sequence.

Expected behavior
The shadda should be centered above the ain.

Screenshots

Additional context
Working in InDesign 2025 on a Mac.

[simoncozens]

This is working correctly in the Fonts web site, and renders correctly in Harfbuzz; I would be amazed if this was not an InDesign bug. Are you using InDesign ME?

[MatthewWilliamsCMH]

Thanks, Simon. Very odd. I am using the ME version of InDesign. I'll post it to Adobe. I've only started working with variable fonts, so perhaps this problem will show up with other variable fonts, too.