Hello
same pb as you here with CB 1.0 and Win7 .. (but works fine with 0.98)
the pb is with the boundary polyline ; if you remove the point shown by the arrow on the picture (*), it will works. It work also if you use
arc fit with tol = 0.002 OR with a remove overlap = 0.002
with a remove overlap, we get exactly the same number of points than the source polyline but with very very small changes.
only 2 points change
the first one (X,Y,Z,bulge)
-4.398301601 -0.710189521 0 -0.039234464
the bulge is slightly different in the "remove overlap" result and we get
-4.398301601 -0.710189521 0
-0.039226404and the last one ; Y and Bulge are also different
-4.399999976 -0.723110735 0 -0.065444594
-4.399999976
-0.723109615 0
-0.065438969(*) done with Eddy's Insert Points plugin
I don't understand the reason

I guess it's a new bug on V1.0 ...
++
David
Edit: it also works if I round to 7 decimals
http://www.atelier-des-fougeres.fr/Cambam/Aide/Plugins/polyround.html