Editing part group brackets

When I have added two violins, viola and cello in Setup mode, an undesired nested part-group bracket is drawn for the two violins. I cannot figure out how to remove this extra group bracket.

What mode should I be in to edit group brackets? How can I remove the bracket which is grouping the two violins? (see photo).
ExtraGroupBracket.tiff (185 KB)

The options for bracketing and bracing are in Engrave > Engraving Options, but I’m afraid that due to a bug the option to prevent sub-brackets from showing doesn’t work; we will address this as soon as we can.