Inbound CallerID lost (replaced by value of _RGPREFIX) on POTS trunks

We have upgraded to FreePBX 2.4.x (from 2.2). After the update, the callerIDs that had been appearing on our extensions from the POTS trunks started being replaced by the value of the _RGPREFIX variable (Main). After rooting through this forum and others, I am stumped on what has occurred, and don’t seem to be able to find the way back to what I had before.

Could someone point me at the appropriate place to begin my journey back to the status quo ante? That is, I want the callerID received from the PSTN on my inbound POTS trunks (Zap channels 2,3,4…n) to be displayed on my user extensions.

I am thinking that this is a configuration value whose behavior has slightly changed, so I will hold off on posting configs until I get some feedback.

Thanks in advance for any pointers/suggestions.