Hi DaveReid,
You might well be right, I was told it was the squawk. Anyway, the two TCAS involved do have a way of nominating which becomes the master.
Hi Rudderrat,
Yes, I personally think it's high time there was an autopilot or altitude capture software update installed to all aircraft which softened the rate of climb/descent as aircraft approached their cleared level to avoid the sort of nuisance TAs you refer to.