'both' to separate shows UI with three states

[tordans]

Steps to reproduce

1. https://zlant.github.io/parking-lanes/#17/52.49471/13.44110
2. click the segment from the screenshot
   => it shows both, but the north is no_stopping now
3. remove "both"
   => Issue 1: I expected the values of ":both" to be copied to :left, :right, since one of those will most likely stay the same. I wanted to change just the other
4. re-add the values for the south that where on :both before
5. now click on the segment to the left; it has a :both tagging as well
6. now click back to the initial segment
   => Issue 2: It shows the state from the screenshot. But the first section with "both" should not be there

[zlant]

2. This is by design. If specified :both and :right/:left tags, both sections will be shown.

[tordans]

But I removed the both in step 3 which did remove it from the UI so I assumed it also removed it from the local data.

Then IMO the issue is, that when removing the "both" checkmark, the local data should be copied to left, right (see issue 1) and removed from both.