[PyQt] Missing scrollbar signal in QPlainTextEdit?

[Sundance]

Hi peeps,

I'm playing around with QPlainTextEdit and having the weirdest bug.

In my application, I've got keyboard shortcuts to scroll the TextEdit up and 
down by way of the QScrollBar.triggerAction() method, with arguments of 
SliderPageStepSub and SliderPageStepAdd respectively.

I also need to do some stuff when the scrollbar moves, so I bind the 
scrollbar's valueChanged() signal to the appropriate method.

It works all fine when the TextEdit is a QTextEdit.

It no longer works when the TextEdit is a QPlainTextEdit.

This is really bizarre, because the signal is emitted just fine when:
 - I move the slider around with the mouse;
 - I scroll with the mouse wheel;
 - I trigger the SliderSingleStepAdd/Sub actions instead (with Single instead 
of Page).

And before you bring up QScrollBar.setTracking, I used it and it doesn't 
change anything.

You will find a test case attached herein. Click the buttons to scroll up and 
down. Then do the same with the mouse. Compare.

This is with Qt 4.5.2 and SIP 4.9.1-snapshot-20091015 (the default Ubuntu 
version).

Anybody has any idea what's going on there? A Qt bug maybe?

Thanks.

-- S.
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