FOP2 shows the callerid as informed by asterisk Manager events, it does not make it up. I have seen ringgroups display the extension callerid insted of the caller callerid before, not sure if its fixable. It is not a fop2 fault. It is a problem with asterisk/dialpaln and its configuration.
There is a dial option "o" that you can set in the general settings that might help or not, you will have to try. In the general settings dial options add the "o", reload asterisk and try again.
Edit: I think I remember another thing that can cause this behavior, missing manager events, and mostly in Trixbox that has a broken manager permission system. Edit /etc/asterisk/manager.conf and set "all" for both read/write lines. To this before adding the dial option. Asterisk manager must be restarted after the change.
Best regards,
