I experienced this, and it’s because the default driver config for the SpaceMouse tries to “help” you by making the rotate forward and back motion on the SpaceMouse translate into a mouse scrollwheel. this is by far the most annoying thing about the SpaceMouse and the person at 3dconnexion who decided that this should be the default for all applications needs to be fired immediately, and should never again be allowed to hold a job. (OK obviously I don’t mean that, and I hope it conveys the level of annoyance that this “helpful” setting has caused me.)
You can turn this awful behavior off by just unchecking all the boxes in the SpaceMouse axis configuration dialog. The only one turned on by default is the one that tries to make the spacemouse act like a mousewheel in applications it doesn’t know about out of the box.