Well, I have a few theories on how the "new" CHP extender system works.
Again, these are only theories, but have SOME backing based on conversations I've had with state communications techs in the course of my employment.
It doesn't appear that the P25 extenders have any sort of "priority hierarchy" like the VHF units did, in other words, they are full-duplex units that don't "unkey" periodically to check for handheld activity, the handheld can just key up at any time and get on the air, much like a traditional repeater.
That being the case, my guess is that the first unit on scene turns on their extender, and additional arriving units just work through the existing active extender.
-OR-
Each vehicle is "assigned" an extender channel number, and the officers portables are set accordingly. Or perhaps the handhelds are assigned to the vehicle?
Whatever the case may be, there is DEFINITELY a hellacious problem with multiple extenders being on at the same time, as it's much more common to hear heterodynes when an officer is talking on his or her portable than used to be. THAT is an officer safety issue.
Something tells me the state isn't getting the mileage out of this 700MHz P25 extender thing that they thought they would. At least it works most of the time.
Oh, and Paul, probably time to change that post signature, what with UPman going 10-7 and all.