Although there may be a future firmware solution, this appears to be a pretty clear case of a low Voltage drop out that causes something in the system logic to go stupid?
Given the cost of the radios, the number of radios and how much the radios are replied upon, I personally would probably come up with a solution for the problem.
My initial shoot from the hip, did not think on it for long approach would be to use a simple series diode large enough to handle the entire radio load (with at least a 25% safety factor or more) and use a 7 AH 12 Volt gel cell battery on the radio side of the diode to provide a short term stable power source.
Yes the diode will have 0.6 Volt drop across the junction, however, I do not expect this to be a problem even with the charging system not running, but who knows, you may have to try and see if the diode junction Voltage drop is a problem.
If you cannot find a single diode with enough current capacity, you could put multiple diodes in parallel.
So for about $20 in parts you should be able to test this theory and at least maybe get some of these systems on the road and even with a future firmware solution this may not be a bad way to set up these trunks?
6A, 50V Rectifier Diodes (4-Pack) : Diodes | RadioShack.com
Only issue that would need to be worked out is how to turn off radios when truck is shut down for extended periods. Could be a simple master switch after the gel cell battery? Could be a time delayed relay? If the trucks have keyless entry or electronic door locks, could be tied into the door lock system. This might be good as the radios could possibly start up once the doors are unlocked?
If the radios are turned off manually, then this may be a non issue?