Why won't "medium" hyphenate

I am converting a manual from InDesign to FrameMaker. To get the text in FM, all of the text is exported from InDesign to text only, and it is copied from there and pasted into FM.

Now and then there are soft line breaks that I need to delete. This is what I was doing within the word "medium" when I hit the delete one too many times.

Now it seems I have taught FM never to hyphenate the word medium.

It is still hyphenated in the Spelling dialog screen. Here's what I've tried to fix it:

1. I've tried re-applying hyphenation (several times) to no avail.
2. I've tried deleting the word medium and retyping it
3. I've tried adding "me-di-um" to the site dictionary and applying hyphenation again
4. I've tried closing the file and reopening and reapplying hyphenation again
5. I set Personal dictionary to None
6. I cleared the Document dictionary

I'm out of ideas. It's a three-column document, so it's important.

Anyone know what I am missing?

Thanks!!