This was really messing with the document I've used for years to track tax documents, and whether or not they'd be given to my wife (ie, checked off). However, I did find a solution that worked:
Uninstall Evernote
Install OneNote, which isn't so arrogant as to think it should striket hrough text it wasn't asked to strike through.
With this approach, I finished the tax document preparation quickly. I recommend it for anyone else having problems.