I have a trip with the outbound tomorrow and the return BOS-PHL-TPA (both 321s); on Oct 22; I'd managed to snag 23F on both.
So I just tried online checkin and discovered that all my seats had changed! I actually had no assignment on the outbound.
I was able to reclaim my outbound 319 bulkhead preference and amazingly 23F was still open BOS-PHL. No such luck on PHL-TPA -- they'd moved me to 10A (with no-one in 10B) so I decided to stay with that.
I've got certs to burn so upgrade requests are in for all, so this might be moot. Or maybe lucky Mr/Ms 23F will get an upgrade.