[Elecraft] XMIT button not working in DATA-A mode

[Gene O]

K3 -- While in Data-A mode, I press the XMIT button and the unit does 
not transmit fully.  It sort of goes into oscillation is the best I can 
describe it.  I am transmitting into a dummy load at about 20 watts.

I first noticed this while using WJST F8.  At that time I thought this 
was feed back since I rearranged my shack somewhat.

Has any had this problem?

Thanks. Gene, W2BXR