One InDesign file can't find the user dictionary

I've been using InDesign since it first came out and have never had a problem with the user dictionary until now.

I have a bunch of old files I'm updating. I've done about 18 so far with no problem but the most recent one cannot find the user dictionary and I'm at my wits' end.

I have two InD files open. The 1997 file I finished working on yesterday, so now have moved on to 1998. They have similar words in them because they're both the results from dog shows. Coincidentally the pages I'm looking at each have the same dog name which is not in the dictionary. If I CTRL-click on the name in the 1997 file, up pops the list of suggested words and I've added the name to the dictionary.

However, in the 1998 file, CTRL-click does NOT produce the list of suggested words and the name is still underlined.

I've searched through every pref I can find but can't find the problem.

Since adding a user dictionary is in the InDesign preferences (not in the individual document settings) for the life of me I don't understand why one document can find the dictionary and the other can't. I've checked the paragraph AND character styles and they all have the correct dictionary selected in the Advanced tab.