UNSOLVED Observing isCompatible bug when using bezier tool

  • Hello again! My weekend robofont training (self imposed) continues, and I may have discovered a bug.

    I am attempting a live update on the compatibility of two glyphs from different fonts.
    The idea at its most basic could manifest as a red mark drawn to the glyph window canvas whenever the glyph becomes incompatible whilst you are drawing/editing the glyph.

    I am using isCompatible() and a glyph.changed observer

    It reports when I make a change to the glyph, calling a function that for now simply prints the result of isCompatible.

    It works fine if I remove a contour, and it works fine if I add a point to an existing contour using knife, but it seems to crash if I use the bezier tool to start drawing a new contour.

    I have a gist here, please try to replicate the error.

    FYI I found the useage of glyph.changed in one of Frederiks examples (stencil preview), but usage of this observer appears to be undocumented, I would expect to be able to find it at http://doc.robofont.com/api/custom-observers/