Game 1.0.2014. I DO use some mods, but I don't think they cause these... As quite a few others have run into this. :-)
1. Tethtoril doesn't recognize that one has been given a quest by Firebead in Candlekeep. Error in global variable it seems (have corrected this myself and it works).
2. Firebead doesn't neither recognize the player or Imoen in Beregost, nor give the quest to purchase the book (and as a consequence doesn't react if one carries the book when visiting him). Same as above, though a little more tricky to find. Seems that a dialog node has a condition set which not only hasn't got the value 0; it simply doesn't exist when the check for it runs and therefore the game skips it (I removed it, and it works in the sense that I'm able to finish the quest, though Firebead repeats the question every time I talk to him until I actually give him the book).