Spell Checker is not saving as is after altering the mistaken word. To explain in detail when you enter a wrong spell and click CTRL + R Click correct word. It won't save a word as modified. PFA in the below link.

https://community.dynamics.com/crm/f/microsoft-dynamics-crm-forum/405960/spell-checker-is-not-saving-as-is-after-altering-the-mistaken-word

FYI. If you write a correct word and modify it to wrong and then alter to correct. It works. Please assist if have any info over this.