This made me think.

I notice you are creating content with the black window in it. I used to do this before submixes but now I just create a transparent submix in a position on the main image that the client wants and then I use the black file 001 in folder 000 to create a black window where the IMAG shoots through.

This way, you can fade it in and out if you wanted to.

Of course it helps when you're fading if you have an iris in front of your IMAG projector to remove the black level when faded out.

I have always used DMX on Catalyst and I have never seen a line break like you are talking about.