I tried to reproduce, unsuccessfully, with an internal application. When I tab from an edit form field over to the submit (or cancel) button and hit the enter key on the keyboard the loading panel works fine. Same results with IE 9 and Firefox 12.0.
I also tried this with the same results using this online demo
. Try reproducing your behavior with this demo, and post the results.
You may need to post your .aspx markup so that we can see what's causing this odd behavior