Uller
Adventurer
I'm with IceBear here...at first I was with Artoomis, but I don't think you can conclusively say what is the last round of the spell given the wording of the rules and balance wise...I've always thought that Summon Monster was overly weak anyway(especially when cast by a first level caster)...so giving it an extra action seems fairer to me than forcing it to wink out "early".