This bug is present at fe174ae and in master (after af8f2e0 and e59d979) and probably started at e9f03a5
It only manifests when geometries are clipped using agg_conv_clipper.h.
two commits were made by @artemp that were likely meant to fix this, but they did not so I have reverted them until this is better understood:
upgrade clipper to 5.1.5 - refs #1749
closing, keep compile going. will track upstream issues at #1834