Sorry for the delayed reply, Daniel.
With Keyboard Viewer, not only can you close it with the “x” and shrink it with the “-” in the upper left corner, you can make it disappear from view entirely without closing it: Hover your cursor in a corner of your screen, then an indicator will appear and, after it fills, Keyboard Viewer will disappear. You can then hover in a corner again to make it reappear. However, while it is hidden in this way, it is still active and in the Menu Bar you have the option to “Hide Keyboard Viewer.”
In order to keep this crash from occurring, it is necessary to close out of Keyboard Viewer entirely by clicking the “x” or choosing “Hide Keyboard Viewer” in the Menu Bar.