[Modal] not all changes are observed even with `observeChanges: true`

[mvorisek]

Bug Report

When I modify the demo from #2036 with textarea - https://jsfiddle.net/2w493cyo/1/ - and resize the textarea vertically to force the modal height to be greater than the viewport, no scrollbar is shown. But when I change/maximalize browser window size, it trigger some internal change and scrollbar is added, even if nothing in the modal is changed. It seems not enough changes are observed.

Steps to reproduce

1. open https://jsfiddle.net/2w493cyo/1/
2. resize textare by dragging the bottom-right corner to make the modal height overflow
3. notice no scrollbar

Expected result

Actual result

no vertical scrollbar after modal height overflow

[lubber-de]

Fixed by #2477 [Edit, no it's not, see comments]

[lubber-de]

I rejected my proposed changes from the mentioned PR as a fix for this use case does not seem to be trivial (see PR comments)

[mvorisek]

The #2477 PR discovered observing the changed size is easy, but the problem is a modal refresh (called when a change is observed) is currently problematic, it is breaking/stopping a mouse drag.

https://jsfiddle.net/v2q30wsx/1/ confirms an observer itself isn't causing the drag event to stop.