with pale master, the only PrC that increases caster level for spells per day that i have any experience with, you get more spells every two levels, but it starts at level one. So, more spells at 1, 3, 5 etc., not 2, 4, 6.
... Just read the undead slayer description which says you get more spells at 3, 6 and 9. *shrugs* maybe its 1, 3, 6, and 9? or it could acctually be a bug.
-TV