To this GTK+ bug report there came such comment, which clearly states this is inkscape bug:
------- 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.
The lauhcpad bug itself can be seen here: https://bugs.launchpad.net/ubuntu/+source/inkscape/+bug/257685
In hope that developers will get to this issue soon.
Mattias