I don't see a principal problem with the Perl stack and your function getting called again before it has completed, so I suppose the problem lies elsewhere (it's hard to tell though when only seeing a snippet of code taken out of its context).

One potential problem could be that you aren't caring about the return value of call_sv() (which is the number of items returned by the Perl routine). This is dangerous, because if the routine - for whatever reason - leaves a different number of items on the stack than you're expecting/handling (you're handling exactly one item with your POPs), the stack will be messed up...   (not necessarily your problem here, but still something to be aware of).