Having a 40" 4k monitor connected to my desktop, I see really huge mouse cursor popping on my system. I suggest this setting should rather be DPI- instead of resolution-dependent.
Same here: 1) Start with a laptop with 1920x1080 display 2) Plug an external 32" display at 4k resolution (~132 dpi) 3) Open a new application. The new window will appear on the new screen 4) The cursor in this new window appears ~200% larger than cursors of applications previously open on the internal display. 5) More annoyingly, the cursor remains huge if you drag the new window to the internal display (probably a different bug, but still).
I've just reinstalled the SO on a new computer and was just about reporting the same bug. I'm on Fedora 27 and I need to manually set the size (I've opted for 24)
There's not a lot we can do. We set the mouse cursor value to resolution independent, but it's the applications themselves that are calculating what do with that information. Sorry. The situation on wayland is much improved.