I have (and love) the EB one from Target too, but they specifically say you should NOT count on the harness to hold your child in the cart.
However, my DD generally doesn't try to stand if she's in the EB harness; if I just use the shopping cart belt, she's trying continuously.
I hope she has a fast recovery and NEVER does this again!
Jo
DD#1 "JellyBean" 6/08
DD#2 "Ha" 6/10
"Theory is great, but as I'm in the trenches of diapers and dishes and ear infections, I try to relax and focus on what's most important: love."--mjs64