Not sure if this is a bug or I am not understanding the Menhir type.
But I used a Svirfneblin Crumbler on one and it didn't make a save or spell resist or any indication that it was affected by it. Pretty sure they are elementals?
Pretty sure you're right ;)
Description: This spell inflicts 1d6 points of sonic damage per caster level to a selected construct (to a maximum of 15d6).
Crumble is for constructs.
Oh. I thought it worked on constructs AND elementals. Ah well. My bad again.