Comment 11 for bug 166697

> In the attached file (reduced test case), the path data 'd' of the circle segment changes in Inkscape apparently already on load

Confirmed, but not directly related to the extension. The "undoing" effect also works when directly modifying the drawing:
1. Open the file from comment #10 in a text editor. Path4295 has d="m -64,293.36218 a 98,98 0 1 1 -196,0 L -162,293.36218 Z".
2. Open the same file in Inkscape. The path changes automatically and has now d="m -64,293.36218 c 0,54.12391 -43.87609,98 -98,98 -54.12391,0 -98,-43.87609 -98,-98 0,0 0,0 0,0 L -162,293.36218 Z".
3. Modify the drawing (create a rectangle). Path4295 doesn't change.
4. Undo. Path4295 reverts to the d value it has in the text file.

There must be some kind of synchronization missing when initializing the document and what we see (the modified d value) is not what we get (the original ones) if we pass the document to the extensions system.
That said, since that problem is not related to the extensions (and can't be fixed in inkex.py anyway), I suggest we open a new specific report and apply the patch from comment #9 (unless we find performance issues or regressions of course).