[Elecraft] CW Sidetone lost

[Bruce Chadbourne]

Greetings to the List - I am scratching my head on this.
Lately I've been using my new hearing aid interface as a headphone
accessory for my K-3.  It is a small box (Phonak brand) that plugs into the
K-3 headphone jack, and transmits the audio to my hearing aids via
bluetooth.  Works great - I enjoy listening to the bands, direct to my
ears, without bothering the household, and avoiding some local noise
interference.

BUT - when I send CW, the sidetone is absent (and denies me the ability to
listen to my transmission).  This makes no sense.   The sidetone is very
present when I use regular passive headphones, or the K-3 speaker, with no
adjustments to other settings.  As soon as I plug the Phonak in, the
sidetone is gone.  All other receiver audio is coming through just fine.
The problem occurs whether I am using straightkey or paddle.

I'm assuming there's some kind of active voltage coming from the Phonak
into the headphone jack but why does it only affect the sidetone?  Reaching
for the schematic...

Bruce / KE1CY