title: qscrollbar (not a qscrollarea) setValue not working
body: <p>I am working on a qwtPlot and have implemented custom scrollbars to illustrate the position of things on the plot when zooming in (in regards to the whole thing - so basically the percentage).</p>
  
  <p>Now, everything works fine, apart from the moment, when I do any zooming or panning right at the beginning (or simply when I see the whole plot and then I want to zoom in).</p>
  
  <p>This is a slot I am using to refresh the appearance of the scrollbar:</p>
  
  <pre><code>void ScrollHorizontal::refreshAfterChanges() {
  setValue(myPlot-&gt;getLowerBound(QwtPlot::xBottom));
  setPageStep(myPlot-&gt;get_X_delta());
  setSingleStep(myPlot-&gt;get_X_delta()/10);
  setMaximum(myPlot-&gt;dataFromSources-&gt;lastTimeValMicro()-pageStep());  
  update();
  printV("HorizontalScroll::setValue",myPlot-&gt;getLowerBound(QwtPlot::xBottom));
  printV("value", value());
  printV("pageStep", pageStep());
  </code></pre>
  
  <p>in the constructor I set the maximum to 0 (just in case, but it doesn't change anything)</p>
  
  <p>The last 3 lines print out some values useful for debugging. What I found out thanks to them is that the slot is executed correctly, but the setValue(int) function doesn't work as I would expect it to:</p>
  
  <p>//printed values right after starting the program<br>
  HorizontalScroll::setValue=0 <br>
  value=0 <br>
  pageStep=7320<br>
  <p>//printed values after using the zoomer once<br>
  HorizontalScroll::setValue=956.316<br>
  value=0<br>
  pageStep=2225<br></p>
  
  <p>Then, when I move the plot a tiny bit, e.g. zoom it 1.1 times, the setValue works properly and value() return the same thing I set. But if I go to the 100% view (the starting point) I get the same problems again.</p>
  
  <p>Just to illustrate it, here are some screenshots:<br>
  <a href="http://tinypic.com/view.php?pic=2znph7s&amp;s=8#.UvNkDoZhauY" rel="nofollow">http://tinypic.com/view.php?pic=2znph7s&amp;s=8#.UvNkDoZhauY</a> <br>
  (100% view, right before zooming in) <p>
  <a href="http://tinypic.com/view.php?pic=ke7nn9&amp;s=8#.UvNkYIZhauY" rel="nofollow">http://tinypic.com/view.php?pic=ke7nn9&amp;s=8#.UvNkYIZhauY</a> <br>
  (badly set qscrollbar)<p></p>