Can't add words to dictionary

[Mitlov]

I'm trying to add some words to the autocorrect dictionary. My problem is this: when I select the word I want to add, no "plus" sign shows up in the list of words to replace it with.

All the online guides say what this one does: Windows Phone 7 : Customizing the Dictionary - Microsoft Certification Examples, exercises, practises, tutorials, solutions about Windows Phone

But on my phone, an HTC 7 Pro (aka HTC Arrive) running Mango, there's no dot between each word and there's no plus side on the left side. What gives?

 

[Mitlov]

Okay, figured out what the issue is...sort of. If you've already got a word in your dictionary, but in a partially capitalized form (like "SI", the abbreviation for Sports Illustrated), it won't let you add the word in lowercase form to the dictionary (like "si", the Spanish word for yes). I added "Estoppel" to the dictionary just fine, found the plus and everything, but now that "estoppel" is in the dictionary, it won't let me add "estoppel"...what gives?