OS: Windows 8.1 x64 (fresh, installed only 4 days ago)
CPU: Intel Core i7-4770K (4 cores, 3.5 GHz)
GPU: AMD Radeon R9-270X 2Gb
SSD drive

1) What happened
The Unity Editor hangs/freezes when I stop "Play mode". It happens always and only way to release Unity Editor is killing the "UnityShaderCompiler.exe" process (which is using 0% of CPU, 5488Kb of RAM). Then, after 5-10 seconds, Unity Editor become responsive.
The most goddamn thing with this bug - it's also somehow lockdown some actions in OS - for example, opening Context Menu for folder in Windows Explorer is also hangs until "UnityShaderCompiler.exe" is killed!

This never happens with Unity 4.4 and I'm sure it's not related to sockets/threads we're using in the game. But if I open empty scene in this project, start and stop "Play mode" with it - everything seems to work correctly. So this happens only with actual gameplay scenes of our game.

I've reproduced issue - the Editor.log should be included with this bug report.

2) How can we reproduce it using the example you attached
I'm sorry, I can't attach example project, because this happens only with our game project - VoidExpanse http://atomictorch.com - and it's not so easy for us to share full source code of this 1  year project. If it's required, you can sign NDA and then we will share it with you.