gtk-2.8.14 range widget & mouse wheel bug

[Giorgos Keramidas]

Mouse wheel support seems broken in range widgets of gtk-2.18.4 here.
When I *reduce* the value of a range widget by rolling the mouse wheel
backwards, all works fine.  Increasing the value by rolling the wheel
'forward' or 'up' (for horizontal widgets) does not update the value of
the range widget at all.

This is easy to repeat here by clicking on the icon of the volume
control applet in Gnome [gnome-volume-control-applet] and trying to
adjust the master volume using the mouse wheel.  Lowering the volume
works.  Bumping it to a higher value doesn't work at all.

This used to work with an earlier gtk+ version so I will try an older
package tomorrow, to see if I can find the first version that's broken.
In the meantime, patches or suggestions about tracking this better are
welcome :)