ExtJS Version:
IE Version: 11.0.40

We have an ExtJS app using the classic toolkit that has the ability to launch some ext windows as modal (an editor and some info/input/details boxes for example). In IE, the windows are sometimes launched and then immediately go to the background of the app (behind the window that launched it by a button click). Seems that in mouseUp event handler in button.js there is an IE specific defer happening that steals focus.

I've written a fiddle that can demo this (only happens in IE) https://fiddle.sencha.com/#view/editor&fiddle/214q
To reproduce this, you really just have to keep opening windows (the speed at which you open windows does not matter, just seems to be a timing of events in IE). When it happens you the window pops up and goes behind the window that was previously launched.

We've worked around it with an override currently in Component that defers the actual show part of the show method.