Some buildings do not 'allow it' to place the objects (exsactly) where you want them to be, because of their/such moddeling I guess. Also some mods (ECP is well known by this) have a 'habbit' to misplace some in the editor placed objects (if they're not placed with ECP and later played with ECP for instance), sandbag is one of them, but not 50.cal mgun thou ,,, and ,,, height of 260 ,,, are you sure, that's 260 meters dude ...
EDIT: Hm, Arcadia ,,, this is for ArmA, yes? Wrong forum then ...