Produced on Windows XP, SP2; Inkscape 0.46, Apr 1 2006 build
Steps to reproduce:
1. Use the arc/circle tool to create a circle or ellipse.
2. Set Start angle to 0, and End angle to 40.
3. Set Start angle to 40, and End angle to 80.
Notice that although the spinbox for the Start angle displays 40, it is actually using 0 for the starting angle. To correct, you need to change the Start angle to something else and back (press Up then Down on the spinbox buttons, for example), to force Inkscape to recognize the Start value.
Probably occurs because Inkscape forgets the Start and End values when they're set to the same number (you can see the XML attributes for them disappear in the XML Editor), then doesn't recheck the Start value when a new End value is entered, and just uses 0 for Start.
The bug also occurs in the opposite case: set Start to 40, End to 0; then set End to 40, and Start to 80. End angle will be 0 although the spinbox displays 40.
Suggested fix: Make the arc drawing code check both spinboxes if one value is changed and the XML attributes aren't present, or even check both spinboxes any time one of the values is changed.
confirmed on Win32 dev build 20418 from Dec 30, 2008.