Linux: CQUI Trade Screen overlay randomly can't be dismissed

**Issue by [corq](https://github.com/corq)**
_Sunday Aug 06, 2017 at 20:59 GMT_
_Originally opened as https://github.com/CQUI-Org/cqui/issues/609_

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Randomly CQUI trade screen will not dismiss after considering (but not completing) a deal. i.e. I cannot escape the deal screen. This seems to happen if I bring up the trade screen while a turn is completing in the background and the game itself shift the ui in the background. Notably, if I can reach ui elements on the side of the screen they are clickable, but remain obscured behind the CQUI deal screen.


Interestingly at one point this happened and another civ prompted for a deal, and the "original" deal screen was partially visible underneath. At this point, clicking escape dismissed both deal overlays with it, and I was back to the game again. If there is a specific log needed, I can upload. Ubuntu 16.04 Mate.

No source file, test, or entry point is named. Reproduce the Linux trade-screen overlay failure while a turn completes, inspect the CQUI UI behavior and any relevant log, and consider the issue done when the deal screen can consistently be dismissed without leaving an obscured overlay.

Written by the indexing model from the issue text.