[Elecraft] TX_INH input (pin 7 on ACC) behavior

[Brian Moran]

With my early K3, I'm attempting to control the TX_INH line on the ACC Connector, and am finding this odd (to me) behavior.
Starting with the radio off, I'm driving the pin with either 0 or 5v through a 6.6K resistor per the Elecraft manual. I set the TX_INH mode to HI in the config screen, and even with the line NOT driven, TX_INH is indicated by the flashing TX in the display.
If I get out my Fluke VOM, I see that there's around 0.2v measured at pin 7... BUT THEN THE TX INHIBIT goes off (that is, it starts working as described in the manual)?  Is the TX_INH line floated in the radio? 
 Do I need to also "pull down" this line to ground through a suitable high-value resistor? 

Adding a 470K ohm to ground seems to make everything happy. If this is expected behavior (requiring pull down as well as pull up), perhaps this could be mentioned in the manual in the future (maybe it only matters to my era of K3 radio -- #512)

What makes this a little more difficult to debug is that after the line has been measured with the meter, causing it to work, TX_INH sometimes continues to work (High=inhibit, LO=tx). Until I power cycle the radio.
Anyone who has done this before have any insight?thanks,-Brian N9ADG