Comment 6 for bug 1093742

the problem is not limited to just stroke-width. It shows up also in the properties fill-opacity and stroke-miterlimit. It can be triggered in the XML editor without actually moving the object. Attached is a demo file. The original style variables are:

fill-opacity : 0.732
stroke-width : 1.05
stroke-miterlimit: 4.27

To trigger the bug, click on Edit->XML Editor. Select the line and click on the style property in the XML Editor. Note that the style still has the original values. Now click on the Set button. The style properties update to the the new values below.

fill-opacity : 0.73200001
stroke-width : 1.04999995
stroke-miterlimit: 4.26999998

This was done with a numericalprecision value of 8 in the SVG Output preferences, which is the default.
The error appears to be coming from the routine 'write_num' in the file svg\css-ostringstream.cpp. In order to fix this, it would probably be necessary to use some formatting code that is more similar to the code for writing the 'd' parameter for the path data, which appears to be in the routine svg\path-string.cpp.