When auto-complete is turned off, the Editor will not allow a cursor up or down when typing, and at the end of a word.
For example: Make sure you have auto-complete UN-checked in the settings.
Then try typing the following in the editor:
Do not hit a space after typing the p. Just try cursor up or down. It will not work until you type a space, or cursor left or right, etc.
Once you have taken it out of word typing mode this releases the "lock" from up or down.
My guess is it that it has to do with the still partially functioning auto-complete, which would normally use cursor up or down to scroll through the suggestions. (It's still trying to.)
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