[Elecraft] K3 changing split?

[Chris M0PSK]

On a small number of occasions recently I've been working (what I believed
to be) split on CW, and been embarassed to find that I've transmitted on the
DX frequency. At first I put this down to senior moments, but now that I
have had the same thing happen on RTTY, I am increasingly (if not totally)
convinced that the K3 has reverted from split to unsplit of its own accord.
Could this be a result of RF in the shack? I would appreciate advice on
where to start troubleshooting. I am running the latest firmware on an
unmodded K3/100  #328 with the KA3T installed. The antennas are dipoles with
a common coax feed.

73 Chris, M0PSK