Map display not filling window in QGIS on Mac?

In this screenshot of QGIS, you can see that the map is not filling the window. I have tried resizing the window in various ways.

Am I missing something obvious, or is this a bug?

Versions:

• MacBook Pro MacOS High Sierra 10.13.5


• QGIS version 3.2.1-Bonn


• QGIS code branch Release 3.2


• Compiled against Qt 5.9.6


• Running against Qt 5.9.6


• Compiled against GDAL/OGR 2.2.4


• Running against GDAL/OGR 2.2.4


• Compiled against GEOS 3.6.2-CAPI-1.10.2



• Running against GEOS 3.6.2-CAPI-1.10.2 4d2925d6


• PostgreSQL Client Version 9.6.6


• SpatiaLite Version 4.4.0-RC0


• QWT Version 6.1.3


• QScintilla2 Version 2.10.7


• PROJ.4 Version 493


• Python 3.6.6

Answer

This is a bug. Install an earlier version or wait for it to be fixed.

Update: This Mac-specific bug brought attention to the fact that the QGIS has not been as well supported as for Windows as for MacOS. There is now a MacOS specific bug fixing campaign.