It seems that trying to switch between mouses on the computer doesn't work using the tab interaction. The system only cycles through the KCM contents and not the help/reset/apply buttons outside of the KCM. Neither does it seem like it cycles through the categories on the left. This behavior is correct in other KCMs, though I don't have an accurate list of which ones do not work. The expectation is that the user should be able to work through the entire interface using TAB navigation.
Hmm, can reproduce. Seem to work with other QML KCMs though, except for the touchpad KCM.
*** This bug has been marked as a duplicate of bug 471957 ***