"Affects Version/s: Minecraft 1.8.8 " Its NOT the Windows 10 beta
I can confirm this.
Here is a link MC-73057 to the bug report I submitted (marked duplicate .. sorry didn't think it was reported) anyways there is more info in my report that might help reproduce this bug.
To me it appears maybe the network stream is not being closed every time.
P.S. I have personally left the client open for hours after it hangs and it never goes back to main menu.
Very sorry I checked before posting this and could not find a duplicate. Sorry for wasting your time. 🙂
Sorry for the late reply but yes it does happen in 15w31B as well. The fix listed above in the description is the only way I have found to make it work right. That fix also solves other problems with apps displaying blurry for me on windows 10.