The bard, paladin, and ranger spell lists contain a number of spells that don't appear on other classes' spell lists. In general, any character who enters one of these prestige classes should gain access to spells unique to that class's spell list, at the same levels indicated for the standard class.
What exactly does that mean?
Possibilities I see:
Gain access based on Paladin level and spellcasting rate -- IE, gain Bless Weapon on my 1st-level spell list at level 9 (Cleric 6/Prestige Paladin 4) and Heal Mount on 3rd-level list at level 17 (Cleric 6/Prestige Paladin 11).
Gain access based on Cleric+Paladin level and Paladin spellcasting rate -- gain Bless Weapon immediately, and Heal Mount at level 11 (since a Paladin 11 could cast it).
Gain access based on Cleric+Paladin level and Cleric spellcasting rate -- adding all Paladin spells to my list immediately, since at Cleric 6/Prestige Paladin 1 I can cast Cleric 4th-level spells.