The TPV shouldn't stop them from releasing. It's only designed to shut off flow from the air system on the tractor to the system on the trailer in the event of a air leak, break away, etc. This would cause a sudden pressure differential between the lines on the truck and the lines on the trailer which would shift a spool in the TPV and shut off the air to the trailer. In other words it should have nothing at all to do with the brakes releasing. It might keep them from getting air to apply but not the other way around.
On the other hand the combo relay/QR valve typically is designed to use a small volume pilot signal from the treadle valve to shift a spool and in turn send a larger volume of air to the brake chambers from a seperate tank located on the trailer. The pilot and delievery sections of the valve are seperate. As such, if the spool in the combo valve is sticking, it will continue to keep pressure on the brake chambers instead of shifting to dump pressure and allowing them to release as they should, even when pilot pressure from the treadle valve is released. This sounds to me like what is happening in your case. Good luck.
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