BUG - can't add Label/Notes text using magic sheet Command

I'm trying to label a cue using a command button in a magic sheet. I can do this fine with a macro, but it doesn't seem to work with a command.

"Cue Label AFO ◆◆"
This should label the current cue AFO - it works as a macro but when run as a command it leaves "Cue Label" on the command line, without the text and not 'entered'.
If I run the command without the text ("Cue Label ◆◆") it does 'enter' the command, so removing an existing label from the cue.
This seems like a bug to me.
I'm using 3.1 on a mac (Nomad).
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