The moral is: on the A320 NEVER disobey the FD pitch bar in OP DES mode, particularly if you are relying on A/THR to control speed (it won't, because it will be in IDLE mode).
When you no longer want to obey the pitch bar, turn BOTH FDs off, which will (or should...) change the A/THR into SPD mode.
We learned that lesson over 25 years ago...
