After canceling copy mode, a user still can paste cell text

Steps to Reproduce

1. run keikai, click "New book"
2. input a in A1
3. press ctrl+c at A1
4. input b at A2, press enter, A1 is not highlighted
5. press down key
6. press ctrl+v

If a is not pasted, keep doing step 5 and 6

Current Result

a is pasted

Expected Result

nothing pasted since it's not in copy mode for step 4