I'm playing the 1st (since I haven't finished it I don't know if there are more) campaign game as The Endless Night faction.
1) The Berserker's Broadsword says that it grants the Maul ability. But so far in multiple battles, all wielded by Tandis the Warrior, he hasn't struck more than once (i.e. maul) even one time. So it appears that this sword's maul ability isn't working.
2) The Pariden's Quest requires me to return fragments of Queen Procipinee's crown to the Temple of Pariden. The Temple of Pariden is on an inaccessible tile right next to the South Gate, which make it impossible to reach the tower to complete the quest.
If memory serves, the quest target being on a not accessible tile (2) sounds a lot like a bug I reported and that I thought was fixed back in the FE:LH beta.
Edit: Although I had all of Tandis's slots filled, I had not been awarded the Overdressed achievement until I replaced the Berserker's Broadsword with a Shadow Broadsword. So perhaps the Berserker's Broadsword is even more bugged than I thought.