I just noticed this. Not sure if one can call it an issue/bug per se, but to me seems like an oversight of otherwise intended behavior.
After trying to make a cued line of lyrics be above the staff for a cue in an instrumental part, I noticed that changing that property in the cue affected the source material in the score (and all other layouts). After experimenting a bit, I found that any Global Only property when adjusted in a cue can affect the source material of that cue.
The prospect that one can inadvertently (or even purposefully) change the source material of a cue from within the cue itself in a completely different layout strikes me as unusual. I’d suggest Global Only properties shouldn’t be adjustable in cues (the same way I can’t change the pitches or rhythms of a cue). Or, even better, that those properties can be adjusted locally within a cue so that they do not affect the source material anyway.