scottgonzalez/jquery-ui — comment on commit b33282468265a053603fc915a1acfcf6d4ba40fc
File:  line 0
By spekary:

I am looking at this problem too. Its pretty important to fix for using an autocomplete as a combobox. The reason this is not working in IE is due to what appears to be a basic IE problem. The event.preventDefault in IE is not preventing the blur event. The blur event is canceling the selection. This bug is isolated here: http://jsfiddle.net/ZLu7X/3/. This appears to be the same bug as: http://bugs.jquery.com/ticket/10345. Note that there are some workarounds mentioned in that ticket that the core jQuery coders are hesitant to implement.