@trajic ...quick reply (and thanks), but it seems that I am the,,,"trajic" one: I had installed (some weeks ago) an app that erases history/does not allow any new entries on one click and forgot about it. Seems that I accidentally clicked on it's "button" and did not notice (I didn't even remember I had something like that there). Fortunately I saw some post while googling for a solution to my issue, that proposed disabling all extensions, and when I went to the extensions page I saw it there being enabled and obviously preventing Opera from recording history entries....
Feeling like an a$$ I immediately came back here to delete my post, and saw your quick answer, so in second thought, I'll leave it there in case some other a$$ suffers from something similar and my experience will at least help him....