Hi all- while I am not sure this is a bug, it is certainly a limitation in Gcon. Gcon is not lying here, it just is not aware of anything higher than G2 - two co-linear lines are reported as G2, which is also pointless- if it is G anything it must be G infinity.
I would look at the curvature graph for more info about continuity higher than G2, for now at least. If the graph from one curve transitions smoothly to the one on the other, you have G3 - that is, no kink between the graph of one curve and the graph of the next.
-Pascal