Electricaly dogged devices become un-dogged when pushpad depressed


A 3' exit device can not be modified to a 4' exit device. You will need to replace the device with a 4' one.
Yes the Von Duprin QEL exit device retracts the latch bolt and pushpad. Pushpad and latch bolt stay retracted as long as power is applied to the QEL exit device.
Bad dogging hook on the dogging assembly could cause the 33A/35A and 98/99 exit device latch bolt not to retract completely.
Most likely need to length the top rod so latch can engage it's internal latch retention state. See 2390 Instructions for adjusting rod lengths.