>That will certainly help in a lot of situations, but unfortunately the button in question isn't always a cancel button. In some situations it launches a value picking form, and in others it might launch a "define new..." form. In all of these situations, we are fighting with the validation of the current value.

Here's one that might get some Boos and Hisses from teh peanut gallery, but you can use MDOWN() to tell if it was a mouse click, then use sys(1270) to find what object the mouse is over. Depending on the name of the object (or better yet a custom property lNoValid) you can skip the valid().