[PyQt] Slider sender().value()

[Gib Bogle]

Using PyQt 4.5.4, I'm getting strange behaviour with sliders.  Everything works 
as expected when the slider handle is dragged, but not when the Left/Right keys 
are used (this is a horizontal slider).  What happens here is the Left key works 
OK, being able to take the value all the way down to 0, but the Right key 
increases the value a few times then starts switching back and forth between n 
and n+1, where it isn't obvious what determines n, but in any case it's not 
determined by the maximum value set for the slider.  Two slider both have a 
maximum value set at 100.  After moving the slider handle to 0, one slider will 
only move to the right to 2 before switching between 1 and 2, while the other 
goes up to 36 37 36 ...

Is this a known bug, or does it suggest an error in my code?

I'm using PyQt 4.5.4 because 4.7 doesn't work with PyQwt 5.2.0.