What program are you using to broadcast keys?

Most programs can have a key bound to disable broadcasting. I use Octopus, and I have my tilde (~) key bound to enable and disable broadcasting, with a sound effect associated with each setting (A buzz for broadcast on, a click for broadcast off).

Also, you should be able to set your program to only broadcast certain keys. I don't broadcast any of the letter keys for instance, so when I'm chatting with people on one character the other one won't spazz out... although the second one does jump a lot because I always broadcast space bar.

Hope that helps.