I guess it may be by design.
By design? What purpose would this feature serve? Okay, got to admit, "cleaning up" the opened tabs of any forgotten empty ones might make it look more tidy when you open Opera again, but still... I'd love an option to tick, like "keep empty tabs", or something.
Ah, well... gotta wait for it change, I guess. Or for someone with more programming skills than me (virtually none^^) to make an extension that adds that option or changes Opera's behaviour in that matter. Anyway, thanks for the anser