Cannot dismiss/move Overflow Menu in Customize Toolbar if window is wide [RC] [Mojave]

To reproduce:
Go to Customize Toolbar and try to move or dismiss the Overflow Menu. I couldn't do either.
There's no red button.

Does not occur on the Beta version.

Temporary workaround:
Narrow the window horizontally to have the Overflow menu appear at the side.

0.99.126.4.1.8-rc (WebKit 619.1.1)
(This also occurred in previous RC versions)

Mojave (10.14)