Curly brackets (braces) are too large in a score where some of the keyboard parts use small staves.
OS: Pop!_OS 18.04 LTS, Arch.: x86_64, MuseScore version (64-bit): 3.2.3+dfsg1-1~ppa1804+1 (Ubuntu bionic/amd64), MuseScore build number not set, revision: d2d863f
This only affects curly brackets. All other brackets: wing-tip, square, and line, work properly.
I can confirmed that staff names have no extra "Enters"
Also confirmed that new keyboard instruments added exhibit the same behavior.
Also confirmed that the behavior exists whether you select "small staff" or reduce the size of the staff to 80%.
To reproduce: set up a 2p8h score with 4 piano staves. Make the Piano II Primo and Secondo either "small" or scale to 80% (both exhibit the same behavior). The bracket will be too large on the systems with small staves.
Comments
I tired and cannot reproduce the problem there must be something else going on in your score. I tried adding a spacer like your picture shows as well, still couldn't get it to fail. Please attach the actual score so we can investigate further.
No wait, I figured it out, it's only a problem if you use the Bravura or MuseJazz fonts. It works fine with Emmentaler and Gonville.
I suggest you submit an official bug report to the issue tracker (see Support menu above).