I found a trivial work-around for the problem of the MessageBox associated with a G-code (MSG, text) comment being displayed before preceding commands have completed - Simply precede the MSG comment with G4P0.

Though seems to me two nice improvements to this feature would be:

1) Don't display the MessageBox until all previous commands have completed, and,
2) Force the MessageBox to remain on top of the main for, by setting the TopMost property. I've had a few instances where the app became unresponsive, because I didn't realize there was a MessageBox up, but hidden behind another window. Takes a bit to realize what's going on.

Regards,
Ray L.