[quackle] Can't exchange tiles

[eyesee7]

I've downloaded the most recent version of Quackle and find that I
can't exchange tiles.  I'm playing Human vs. "Speedy Player."  I type
"exchange" and the tiles I want to exchange in the play bar at the top
of the screen but the "commit move" button isn't clickable.  I tried
clicking the "+5" button (what does that mean anyway? it used to be
the "enter move" button) and I still don't have the option to click
"commit move" and exchange tiles.  What am I missing?