Can you be more specific? Does it work but it's laggy or is it not functional at all? What OS are you using?

Another user told me about mouse getting stuck under Windows 10. It seems like a platform specific bug. He was on a desktop though, so the problem is not laptop specific.

It's a SDL / Windows 10 FCU bug: https://discourse.libsdl.org/t/win10-fall-creators-update-breaks-mouse-warping/23526
Current mercurial version of SDL has a workaround.

It seems like Windows behaved the same way for the last ~30 years regarding mouse movement events, and then it changed its behaviour in the Fall Creators Update. The behaviour was not well specified to begin with, so it is still in accord to spec, whatever little spec there is. This caught other programs and APIs with their pants down.

The following appears to be the official Microsoft way to deal with relative mouse movements: https://docs.microsoft.com/en-us/windows/uwp/gaming/relative-mouse-movement

This is not an IBMulator's bug, rather a SDL's bug. I'll do a binary release with the most recent SDL version.

This issue has been addressed with commit 6f09e0b.