Open attachment 180550 [details] from bug 149440. Save it to new file. Compare the original and the saved version. The attribute draw:glue-point-leaving-directions is lost on saving.
Even if using the attribute is not implemented (see bug 149440) LibreOffice must not lose it. Preserving the attribute is possible, because the needed property exists already. It is GluePointLeavingDirections in service EnhancedCustomShapePath.