From Lou KI5FTY, posted on the uBitx Forum:
"Found the problem with the transmit with trailing tone. In memory manager you can set CW DELAY (TX-RX) and it was set to 0. One would assume no delay. Not true, it must use some system default. Changing it to 1 (10ms) shortened the relay hang time to an noticeable amount and the wave form looks ok. 2 Questions:
1) is that a bug or undocumented feature ;-)
2) why would there be tone output while the relay is closed but no keyup?"