Comment 6 for bug 257685

Copied from gnome bugzilla:

------- Comment #1 from Matthias Clasen 2008-09-04 00:47 UTC -------
GTK+ is simply enforcing documented behaviour now. The fix is to set page_size
to 0 when using adjustments for simple scalar values, such as in a slider.

>From the release notes:

* GtkAdjustment now enforces that values are restricted to the
  range [lower, upper - page_size]. This has always been the documented
  behaviour, and the recommended practice is to set page_size to 0
  when using adjustments for simple scalar values, like in a slider
  or spin button.