As I found out before, the Elecraft K2 uses the same signal line for PTT input and for one of the Key lines (dit I think). This is a royal pain when integrating into a more complex arrangement such as a computer controlled station, or an SO2R contest station. In these configurations, you are likely to be using interface devices to drive the PTT line, and not a Microphone. I am using my K2 for both remote-control and SO2R contesting, so I had to find a way to easily handle this problem.
When operating SSB only, this is no problem and can be ignored. If you are just connecting a Mic and a Key, it is also not a problem. The issue is when you connect interfaces and want the computer to provide the Mic audio, PTT input, and CW keying. When switching between modes you can disconnect the Mic connector any time you want to use CW. Of course this is a nuisance and puts undue strain on the Mic connector.
I am using N1MM contesting software with the parallel port (LPT1) providing the CW and PTT lines. What I discovered is that you can Configure the LPT1 port to control only the “other radio” and the PTT line no longer activates. So if I have the K2 as radio #1, I use the Config Tab in N1MM, assign LPT1 to radio #2, and the problem is solved. Of course I have to change it back when I change to SSB mode, but at least it is quick and does not involve hardware.