if anyone could tell me where in COnsole logs I could find the precise record of what's happening on these uncalled for restarts, I'd be happy to post
I observed the same problem on my iMac Retina 27. The console logs
06:41:46.036209 +0200 powerd Sleep Failure [code:0x11105000400001F]:
Disable FileVault is a working und for this bug on my system.
There is also a thread about this issue on the public Apple forum