Wrong popup positioning during window resize

How to reproduce:
1. open https://jsfiddle.net/ze4rn61k/1/
2. be sure that button in the html pan is visible and far enough from window border
3. press the button (you should see a popup) and start to minmize window from right to left

Expected result: popup should be the same after resize
Actual result: popup is corrupted

Correct popup view (before resize):

Corrupted popup view (after resize):

Start by reproducing the popup resize case in the linked JSFiddle, then trace the repository's popup positioning and window-resize handling; the issue does not name a source file or test. Done means the popup retains its correct appearance while the window is resized from right to left, with a regression check for the reported scenario.

Written by the indexing model from the issue text.