2.71 remapping UVs on file from ealier version(s)

Working on my muscle emulation system I have now had Blender 2.71 three times rewrite my UV map slightly, when I have done no mesh editing that would affect the UVs directly at all. Here’s what the UV map looks like now:

The UV map was produce quite a few versions ago but as of 2.68 I have never had a problem with it. The re-written portions have been exactly the same each time. Is this a known issue or should I submit a bug report?