I have equipped Pellegina with St. Ydwen two-handed and noticed that I did not get accuracy from the sword. On top Pellegina did not get the boni +6 accuracy from weapon talent "soldier" (even it is a "two hand").

 

So in total I am missing +14 accuracy.

Did you look it up on the character sheet or did you check the combat log? Because sometimes the UI of the char sheet has a glitch where different ACC bonuses don't get displayed - but the ACC value will still be applied when fighting (see combat log).

Well, this is really strange. I have loaded the same savegame, but now the stats are fine. And I am pretty sure, Pelegina was not cursed with negative spell, otherwise I would have seen red numbers...I have to check whether there was an update being automatically installed...

That happens from time to time.  If you look at the combat log its always right.  To fix it on your char sheet do you what you did.  Log in and out.