I just tried my KDE 4.8.3 Live-USB and got the same error. I tried reinstalling gtk 2.0, but still no go. To reproduce this error try:
Select the Create Rectangles and Squares tool,
Make a square,
Choose the Edit objects, colors and gradients,
In the fill tab, choose the linear gradient,
Click on edit
Click on the gradient and see the stops click on one and then Inkscape crashes.
I can add a stop and delete a stop but I cant edit the stop.