Found the problem...The full thread is here.
Looks like its caused by linked spell timers. Any item that is activating a PC spell that has a linked spell timer will use up the timer for any other spell on that same timer (including itself). It's just how linked spell timers work.
There's about 30 items that are affected, including the DA hammer. To fix this, I'm going to create new versions of the spells that aren't PC usable and attach those to the items. Should go out next time we patch items and spells to live servers.
Rashere, Lead Designer
Friday, January 05, 2007
Item / Spell Timer Issue To Be Fixed
This problem affects all items which cast or proc a spell which is the same as a player cast spell. It was mainly noticed with the DA hammer. Characters who cast the DA spell found that the DA hammer would not proc during the 15 minute DA spell refresh time.