This post has been up for over a year and I just now noiced it. I have another idea. I use it to "intercept" the keystrokes in a Promt-With-List widow that I put up with KBM. It only works for the FIRST keystroke when that window goes up.
Before going into too much detail I need to ask, @mz94, Michelle, is this still a problem for you? And in your original problem, do you need to always, always, always, capture/intercept the problematic keystrokes, or only when the Media Item Properties window first appears?
I described my method originally in MACRO: “Follow Menu Choice with Return” (v0.5).
Briefly, before putting up the Prompt With List, I activate a dedicated KBM Macro Group for one keystroke. I your case, Michelle, you would have that triggered by the appearance of the Media Item Properties. At this point, with Media Item Properties frontmost, your very next keystroke, and that keystroke only, will be available to trigger macros in that dedicated macro group.
In that group, you can have multiple macros. You can have one macro for each keystroke that you want to intercept, each triggered by one key, or one macro that has numerous triiggers. (I chose the one-macro route because I wanted them all to do the same thing when triggered and editing one macro is easier than doing the same edit to 30 or more macros.)
In the "intercepting" macro(s) you can do a lot of things. KBM has caught the trigger before it got to the app (the Prompt-With-List window). I can now send the app whatever I want. In my example above (v0.5), what gets sent is the value of the trigger followed by a Return character. My own usage has evolved to where I first check if the trigger is capitalized or not, so I can send out different strings in either case (I haven't published that version yet).
In your case, when the Media Item Properties window first appears, there are a bunch of keystrokes you don't want it to get (and you want everything else to behave as expected). Activate your dedicated MIPWindowKeystrokeCatcher group. Inside that group, have a macro (or a bunch) that is triggered by those pesky keystrokes that will do unwanted stuff if they get to the MIP window, and have those keystrokes, and those only, do something like (as above) put a rectanguar highlight around the MIP window for a second, or whatever. Those keystrokes will be gone, gobbled up by KBM's trigger catcher. All non-trigger keystrokes will be passed along, to the MIP window if it can handle them, the main app, or whatever. Non-triggering keystrokes are not gobbled up, they get passed along.
This method only works to catch the first keystroke after the MIP window appers, but I suspect that that is the situation that is the real problem.
I hope this helps.