Yes that did it Jason. I'll make sure I remember that.
What I did was I added a second MRT to the page for a second multi select list. It didn't work and so I deleted it and then found the original didn't work either (this was because, as you said, the wa_appbuilder_php.php file had been overwritten).
I've now successfully inserted two MRT's to the same page using the updated wa_appbuilder_php.php file. Just for the help of others, I deleted the "go to" URL on the first MRT and added it to the second.
Brilliant!! Don't you just love WebAssist :-)