They can also be unsummoned by clicking on the summoning doll again.
Did you try having your other character do the summoning? I don't see where that would make a difference, though. Have you selected the skeleton and moved around? Maybe running him out of his range and resummoning him right away would have a different result? (he would be paralyzed for a short time after coming back)
<img src="/ubbthreads/images/graemlins/confused.gif" alt="" />
