I don't know if there is an official explanation, but basically all magic except certain holy mana spells fail against noncorporeal undead. Mindblast is an exception to the apparent rule, and clerics aren't overjoyed about that, but we don't spend alot of time complaining about it. TK does work if your projectile is blessed, which is logical.

Anyway if you are looking for the logic, look towards needing blessed weapons to hit a non-corporeal undead- its based on the same logic. Holy magic apparently can reach the 'plain' or 'dimension' that these creatures at least partially reside in.

From an OOC point of view- it helps differentiate differant kinds of magic. Sort of why we can't teleport or far see.

Flavius