Ok, so far I have encountered several bugs.
1. The first is that Iorveth dissapears in Vergen so I cannot properly finish the succubus sidequest.
2. I killed like a hundred harpies and didn't get the knowledge necessary to make my own conclusions and be able to use those damn harpies traps or the mythical firefly bombs. The book didn't help either. Got the traps, the bait, but it doesn't do anything when I set them even close to the nests. Another quest broken.
3. This is a game breaker. After the fallback on the wall in Vergen we repelled one attack (I don't know if the second too, because the enemies just kept coming. Now I have been waiting for ten minutes and the enemies just stand down in the courtyard, while the defenders stand on the wall screaming offenses to the attackers. Can't talk to anyone (no dialog options), although you can hear the generic responses (kill them!, "nice ponytail", and so on). The journal says I am waiting for the second wave, but so far it hasn't come. Saskia doesn't talk so she cannot give me the next quest if there is one. Zoltan doesn't talk either. Seems I'm stuck. As I told before - A game breaker.

A reload helped with No. 3, so seems I will be able to continue playing. Anyway it was a bug.