CUA marking stuck when trying to pass BOF/EOF

When marking inside a file with Shift-↑ or Shift-↓ and hitting begin or end of file, respectively, the “shift marking mode” sticks around even to normal cursor movements.

This is likely because macro processing sticks as the second operation returns an error. It definitely only works if you attempt to move one line _more_ than the file has.

No idea yet how to fix this…