This is happening with all of my ActionSheets, Pickers, selectfields. Was working in 126.96.36.199, broken in 2.1.1. Sometimes they fly off the top of the screen and then come back, sometimes they disappear entirely and just leave a blank screen which breaks the app entirely. A quick search of the forums shows that this has been buggy for a year.
Couple of easy ways to reproduce. Take the bottom-docked tab panel example, add a card layout to one of the tabs, add a FormPanel to one of the cards, add a selectfield to the form. Works ok the very first time you click on the selectfield, but then cancel it and try to select it again and it breaks from that point on.
On another card, add a button or link or something that opens a Picker. Same behavior.
Also on the same bottom tab panel, add a Container to the Viewport with a toolbar docked to the top, with a button in the toolbar that creates an ActionSheet. Show it and hide it a few times. Same behavior.
If I add a hide listener that destroys the ActionSheet after a brief timeout, that works, but I need my form elements and Pickers to exist.