Experienced the same issues after splitting the stack and resetting each back to factory defaults. Next swapped the two units (making the non-base the base and vise-versa). The problem actually moved to two other ports, but also on Unit 2.
According to Avaya there is a wi number issued for the problem (ie, it's a known issue), but from the questions being asked by support, I'm not sure they've found a root cause.