Problems entering text with a braille display

Hi everyone. I have a HumanWare Brailliant BI40X. When I got it, I was shown how to use it with an iPhone, including entering text. I exchanged text messages with my trainer. I know it worked, last October.

Since then, I've primarily been using the display to read NLS books. In other words, I've been using it as a standalone device, not with my iPhone. But now I want to get up to speed on using it with my iPhone. AppleVis and the Apple documentation have been great, except for one problem.

I can't seem to enter text in a text field. For example, I open the Messages app, select a conversation, and navigate to the text field. I select that text field (either with one of the cursor routing keys, or with Space+dots 3 and 6. But when I start typing, the characters appear for a moment, then vanish. If I type a word quickly, it vanishes immediately after I hit the spacebar. After I've typed my entire message, there's nothing but spaces, and I verified this by hitting backspace - all I hear is "space, space, space" for each character I delete.

I did a cursory search of AppleVis for a problem like this, but came up empty. Anyone know what I might be doing wrong? I figure it has to be something obvious, because, as I said, I know this worked months ago when I first got the display.

Thanks for any help.