FIXED. SOLVED. Opera 36 crashing and restarting.
Disconnect the network.
Do some editing in bookmarks. Empty trash folder.
Close Opera. Reopen Opera.
Everything runs fine. (At least in my current environment(Linux).
I don't know if this simple step may have solved the issues in my other systems (I just noticed this morning in two systems. No problems noticed in my Opera Android.
ps. While writing this post Opera has updated/synchronized bookmarks with the server. It has restarted it by itself, crashed once, but now is running fine (now checking my corporate e-mail).