Hi,
I think I have seen this before. It is not a Mojave thing, it is cause by the BIMobject Add-on (the BIMobject toolbar to be more specific). The separators are not placed inside the toolbar properly, and they behave this way.
Please try turning off the BIMobject toolbar, and see if it helps. If it does, then please contact BIMobject about this, so that they can fix it in a future release.
Regards,
Daniel Alexander Kovacs
Professional Services Consultant
GRAPHISOFT
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