Kudzu I have not seen a problem like this and I fly the b24 a lot. Some things to check, insure that the autopilot light is lit when it starts to climb.
If it is off it is possible that your joystick is spiking and turning off auto pilot.
you also might try change the dead zone on your joystick. I do know that if the auto pilot is off at altitlue the plane will climb but very slowly.
Maybe some one elese has some ideas of what maybe causing his problem. You also might try filming the failure anns sending to HTC
Regards...................... ...........DarkHawk