I can reproduce this bug easily everytime in the demo page. I did exactly as you said.

Went to demo page, clicked New in Version 3.7, clicked Multiple search, clicked the search icon in the bottom tool bar, this pops up the search form, entered 3 spaces on the right search box and clicked find. The grid shows loading and hangs forever…..after that you can't do anything on the grid , no button works.

Please let me know if you need more information.