GROUP() and GROUP_COUNT() issues with call parking

I limit the number of to/from PSTN channels that can be up at a time. To help enforce this I use GROUP() and GROUP_COUNT() on calls coming in from, or out to PSTN. Works fine in all scenarios except for any phone that is using parked calls.

GROUP_COUNT() does not seem to recognize parked calls. If I output the GROUP_COUNT to the CLI after I park a call, it does not increment. Why is this?

Provide configs and verbose logging.