I use the following piece of code to check my elevator on sit on prim that i compare to the sit target and it delivers a wrong value if i sit on a prim with an animated texture.
vector checked_prim_landing = llList2Vector(
llGetObjectDetails(
llGetLinkKey(checked_prim),
[OBJECT_POS]
),0
);
Prims with no animated texture report the correct value.