Problem of repeat letters when running event handlers

When I add an event listener (e.g. beforeDelete to every rectangle see below) using applescript the handler runs OK.

But when I then type into a text frame in the same document I start getting random repeat characters (e.g. repeeat chaaracters).

The same applies to other event handlers I've tried (afterActivate and afterSelectionChanged).

Is this a bug or am I missing something?

Mac OS X 10.7.4, InDesign CS6.

>>>>

tell application "Adobe InDesign CS6"

          tell document 1

                    tell every rectangle

                              set myPixEventListener to make event listener with properties {event type:"beforeDelete", handler:my doPixhandler, cancelable:true}

                    end tell

          end tell

end tell

on doPixhandler()

          tell application "Adobe InDesign CS6"

                    prevent default evt

          end tell

end doPixhandler

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