The innate level of a spell is it's lowest casting class level, typically. So this might not be a bug.
Attempting to cast Vengeful Mount on a Greater Spellbound Wand does not allow the spell to work. This is presumably a hostile targeted spell, and it's lowest casting classes are Hexblade, Ranger, and Paladin 2. The spell should therefore have an innate level of 2, and be able to be imbued into a Greater Spellbound Wand.
Exact Error Message:
Angela Amana casts Vengeful Mount
Failure! You cannot imbue Spellbound Wand (Greater) with Vengeful Mount.
Vengeful Mount cast with CL [30] Spell ID [1870]
Edit: I've done with with other spells with different innate levels than I'm casting them with as a wizard, so I know this works.