I see that several people are experiencing the same error.
Well, it doesn't appear to be a sticky key, the same behavior occurs using the "Edit, Split At Cursor" menu.
Looks like the error is related to "Tabs" closing.
Everything seems to work fine until you close one or more tabs, the next time you use "Split At Cursor" you get this "error".
Closing two tabs gives you 2 "blank" sections, 5 tabs get 5.
Poorly explained, maybe my screenshot is better?
Svein