Just a quick report on a bug that is causing weird paths to be drawn when using the Offset tool. If I use it on certain curved paths, and set the path to 0% position, it will draw an extended curved line beyond the end of the path. But if I notch that to -1%, the path returns to normal, though I loose a fraction of width in the process.
Also I am using Glyphs 1.3.26 (530) on a Mountain Lion 10.8 Macbook Air 13" 2013.
Could you send me the .glyphs file?