Modem reconnects to same provider after setting preferred list (AT+CPOL)

I am using AT+CPOL to restrict the providers my cellmodem connects to. When I force reconnection (or reboot the host), it reconnects to the same provider that is not on the list.

How do I reset/disconnect such that it will pick a provider from the Preferred Operators List?

I should add that after some time a reset does seem to have the desired effect. Some kind of internal state?

could you pls tell us the module type or firmware version?