Because it might break applications in a way you would not expect from a "compatible" version and the signal is a sensible thing. Sending an unnecessary signal is of course not correct - but not totally wrong.
But maybe you can also go with the QwtScaleWidget::scaleDivChanged() signals. Those indicate any change of the axes ( regardless of being initiated from the zoomer or something else ) and are often the better approach anyway.
Uwe
Any signal has to work only if value changed
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