[Elecraft] Weird AGC Behavior

[David Inger]

Has anyone experienced anything like this?
 
 I am using a K3 (FW version 4.39; DSP version 2.73) with a KPA500 amp
connected to the K3 with the Elecraft AUX cable.
 
I normally have the AGC set for AGC-S when operating SSB or digital modes.
If the K3 is in receive mode for several minutes,  the AGC turns itself off
without warning (accompanied by a hugh volume increase from the speaker).
While this doesn't happen every time, it has happened several times.  It
seems to be most likely to happen if the Noise Blanker is turned on and the
KPA500 amp is on and ready for operation (as opposed to being in standby
mode).
 
When I installed my KPA500, I upgraded the K3's firmware to the above
versions.  I have no idea what is causing the AGC to turn itself off, or if
it has anything to do with the firmware upgrade, the amp, or both, or
neither.
 
I would appreciate any help that exorcises this demon.
 
73 de K6SBA
David in Santa Barbara CA