When e.preventDefault() is not preventing....

[nachid]

I am doing this directly on the ajax demo page. so you can test it for yourself.
I used firebug console and I binded a select hander on the panelbar.

$("#panelbar").data('kendoPanelBar').bind('select', function (e) { e.preventDefault(); });

You can see when you click on a panel, it is expanded and the underlying ajax call is made
The preventDefault is not taken into account.

I had to use recursion to make work as it is supposed to

var event= $("#panelbar").data('kendoPanelBar').bind('select', function (e) { event.preventDefault(); });

[Kevin]

I was trying this out, as I also wanted to disable selection in the panelbar.  e.preventDefault() didn't work, even with the recursive technique.  The following worked for me:

var panelbar = $("#panelbar").data('kendoPanelBar');
panelbar.bind('select', function(e) { panelbar.clearSelection(); });

(Note: I just wanted to disable selection, not expansion.)

[John]

try having your function return false instead of calling e.preventdefault.  I've had to do that when adding an event to the grid refresh button.