SUMMARY

The cursor changes whenever it hovers a KWin control (including title bar context menus, the menus that appear when left-clicking a window icon, and moving the cursor over the alt-tab menu): it approximately doubles in size.  Looks like somehow KWin thinks it needs a high-dpi cursor theme when it does not?


STEPS TO REPRODUCE
1. Right-click a title bar, and hover the menu that appears.

OBSERVED RESULT

The cursor doubles in size.


EXPECTED RESULT

The cursor should stay the same as it is for the rest of the system.


SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 5.14.5
KDE Frameworks Version: 5.54.0
Qt Version: 5.11.3

ADDITIONAL INFORMATION

My internal laptop screen has a resolution of 4K, but I am using it with 1920x1080 (I change between internal and external screens a lot, and with KDE seemingly not supporting dynamic zoom factor changes, that's my only option).  Also, my laptop is one of these weird "reverse prime" machines where the external HDMI port is connected to the NVidia chip, but the internal screen is connected to the Intel chip.  I am using SDDM, and added the following to /usr/share/sddm/scripts/Xsetup :

xrandr --setprovideroutputsource 1 0
xrandr --auto

So SDDM starts on my 4K internal screen, then the external screen gets added (which SDDM does not handle very well, but that's SDDM's problem), then I log in and whenever KDE applies the stored screen configuration the resolution changes from 4K to 1080p. In the midst of this, it seems like KWin gets confused about the cursor theme.