Some companies switch off the FDs at the first sign of traffic conflict - when TA is received. This is in order to be better prepared for what may turn into an RA so one less thing to do if the RA is received - just follow the V/S command.
ps Why cant Airbus modify this heap of cr*p and put it on the PFD like all modern aircraft. The A320 display is the same as that for the old DC9 and B737 when TCAS was first invented. Of course, I forgot, "not invented here in TLS"