Android ignoring imported dictionary
Add 2 more words to your personal dictionary (accessed through Settings -> Language and Input -> Personal Dictionary) and give them optional shortcuts. This will make Android start using all of the rest of the words in your personal dictionary again.

(Also make sure that Google Spell Checker is the default spell checker, also accessed in Language and Input settings.)

This might sound like strange advice, but it worked for me.

Here's what I did, as I recounted in my comment above: So I tried to recreate your problem. I added a word to my personal dictionary, with no shortcut, and when I typed it, it got the squiggly red line! Strangely enough, once I added two more non-words to the personal dictionary (accessed via Settings -> Language and Input -> Personal Dictionary) and gave them optional shortcuts, the first word, still without an optional shortcut, was actually added to my dictionary and lost its red line. And any further words I added to the dictionary worked fully, immediately. So try adding two random English words with shortcuts to your pers. dict.