Open about window
(For reference put deattached some other window next to it, e.g. Console)
Switch focus to some other window that does not cover anyt of them

Steps to reproduce:
1. Open Unity and open About window (Help->About Unity...)
2. For reference - detach some other window and put it next to the About window (e.g. Console)
3. Switch focus to any other window, which does not obscure any of Unity windows completely

Actual result: About window disappears (See https://gyazo.com/9d8838b4d6262aeeb6750faa64317fc9)
Expected result: It does not disappear

Tested and reproduced with:
Windows 10
Unity 5.1.4f1, 5.2.4p1, 5.3.4p1, 5.4.0b12