PHP + Oracle persistent connections problem

I have recently enabled persistent connection from our PHP application to Oracle by using oci_pconnect instead of oci_connect. 99% of the application works fine, but one specific script has problems. The problem is that I bind some variables by using oci_bind_by_name and I get an error that those variables are not binded. The script works 100% without persistent connections, and sometimes is works sometimes is does not work with persistent connections. Is there a sharing of bind variables when I use persistent connections, and multiple requests to the same script reset each-other's variables, or something similar to that? Otherwise I can't find out why it works sometimes and I can't predict the error.