[Elecraft] K2/100 and KAT100 odd behavior

[Floyd Sense]

Here's an odd one I ran into last evening while operating in the 160 CW
contest.  The problem I observed was that if everything was tuned properly
for the bottom end of the band (say, 1805) then moving higher up in the
band, around 1845, resulted in a temporary high output situation.  While
trying to pin this down this morning, I removed the amp from the system and
fed the K2/100 through the KAT100 to the dummy load.  With the K2 set at 50
watts on 1805, I hit the TUNE button and the KAT100 quickly showed a 1.0
SWR.  I then moved the VFO to 1845 and hit the key.  The output was 120
watts!  Sending a string of dits, the output slowly stepped down (discrete
steps, not a gradual decay) until it again read 50 watts after maybe 15
seconds.  If I repeat the test and first press TUNE at the new frequency,
the KAT100 doesn't cycle since the 50 ohm load hasn't changed, and it shows
a 1.0 SWR.  Hitting the key for a string of dits at that point results in an
output of 50 watts, as it should be.

The KAT100 works properly in every other way, and there is no problem with
stray RF getting into cables.  The problem doesn't exist on any other band.
Any ideas as to what is happening?

73, Floyd - K8AC