Simulacrum seems to have the same issue for me. I read the forums and people talk about a simulacrum army. I don't really understand what's that supposed to me. Reading the spell, i know i'd never allow more than one simulacrum anyway, under any circumstances.
But still, even ONE simulacrum is a problem for me, because it doubles someone's power. If the encounter was carefully balanced for a party of four, having a fifth level 14 member will skew the balance, and guess what? I either design encounter for a party of five (for a net difference of 0 for this ability for which a PC has spent resources) OR i don't take it into account and guess what? An encounter designed for four people that actually has 5, is over as soon as it begins.
How do you guys deal with that? I'm really curious.