Windows 10 Pro 64-bit / 1070 Ti / 4k Monitor
Broken: 2.79b, 2.80 Alpha 2 (121c94b0829)
Short description of error
Mouse cursors are "crushed" and turn into very small, black cursors.
All the images are taken at the same monitor size / scaling.
Exact steps for others to reproduce the error
Unfortunately I have not managed to find a reliable way to reproduce the issue.
From personal experience, it occurs often if the computer has been in use for some time, and Blender is then opened. Opening Blender right after boot does not seem to have any issues.
One way to remedy this issue is to override the custom mouse cursor behaviour in the wm_cursors.c, as noted in the Blender StackExchange thread.