Suggest you research the Bangalore A320 accident... I think this was the basis of it
True.
There were a few accidents where Airbus reacted my modifying various flight modes or MCP/FMA indications.
When the A320 was first certified only turning both FDs OFF activated the A/THR SPEED mode. Turning one FD OFF removed the FD from that PFD but the active A/THR mode was as determined by the active FD. If you didn't follow the FD commands you could, and some obviously did, get into trouble. Now turning a FD OFF does not remove FD commands and appropriatre modes remain displayed. Turning both OFF forces A/THR to SPEED, neither FD is displayed and A/THR will target the selected or managed speed and therefore provide some form of protection.