Seat change mystery

My seat request for my upcoming flight on a 747 Config 4 has been in place for six months - seats 12A & 12K

Logging on yesterday I find that we had been moved to 14A & 15A - no problem at all but I now find that 12K has become available again

I know that seats are not guaranteed and can be changed for a variety of reasons but I cannot understand why this has happened ?|

[Nottingham Nick]

I went through a phase where this seemed to be happening to me every flight a few days before I was due to fly. n(

I always managed to swap back to my original seat, and never received any plausible explanation as to why it happened.

Nick