This might help you make up your own mind if the Plex IDE was even designed to G&B with action diagram open STATE ID GENERATION CONFLICT
"When the Panel and/or Action Diagram editors are opened, some of the panel
elements are not read from disk (this was by design). Whereas when the
panel editor and Action Diagram editors are closed, the C++ generator reads the all the
Panel elements from the disk when loading the Panel design."
I don't advocate the practice of G&B with panels and action diagrams open, NOT because I think having them open is unreasonable but because historically there has been some bugs associated with this practice see Parameter Generation Bug in Plex r7.0, r7.1 and r7.2 or INCORRECT SOURCE GENERATION WITH AD OPEN
Close the AD and or Panel and never need worry again..