The ListView control throws an exception in Single-Selection mode, if you ctrl-click the selected item to de-select it. You can see this in the ListView Binding example: http://www.sencha.com/examples-dev/#...istviewbinding. I haven't tried any of the other selection modes to see what they do.
I expect a SelectionChangedEvent<T> with an empty result list.
Thanks for the report. I've filed a bug against the team.
Running the Explorer in development mode, it seems that this is an issue with the way the example has been written rather than a problem with ListView itself. If you look at ListViewBindingExample.java:91, you'll see that the example always attempts to retrieve the first item in the selection, even if the selection is empty (that is, has no items).
This bug has been fixed in the Ext GWT 3.0 Release Candidate. You'll see the corrected List View Binding example in the RC Explorer Demo. While we're confident that we've addressed this issue, please reply if you notice any continued problems after upgrading. Again, thanks for taking the time to report this bug.