[Elecraft] K3 - erratic keyer behavior serial related

[Nick-WA5BDU]

This morning my K3's keyer is behaving erratically - long dashes from 
dash paddle, dashes from dot paddle, gaps in strings of continuous 
dits.  This is my first time transmitting since installing the most 
recent firmware a couple days ago.  I had HRD connected at the time.  
The stuff I've tried -

Backed down from 38k to 19k and eventually 4.8k on the serial port.  
That didn't help, but the keyer works OK when the serial interface is 
not connected.  My serial port is the Elecraft supplied USB to serial 
dongle, plugged into a laptop running Vista.  I tried going to my XP 
computer with real serial port and HRD, communicating at 4800 baud, but 
no luck there either.  Also tried turning off QSK and turning off VOX.  
In case of RF interference, I transmitted at 5 watts into my dummy load 
and also went into TX standby mode.  The only thing that has worked has 
been to have no serial connection.  Oh yeah, my speed is 22 WPM.  And 
the erratic sending also occurred while sending a memory message.

I haven't tried going back to the previous firmware yet.  Any ideas?

73--Nick, WA5BDU
K3 #1195