The mcmod.info for the extended mod has the mod id as "gravestone" which is the same as what is in the base mod's mcmod.info, causing issues with tools that read these files (such as FastPack for MCUpdater).

Additionally, both the base and extended mod have the mod id coded as having mixed case, which as you may have seen, produces a warning in the logs on startup in 1.10.2 as only lower-case mod ids are allowed in 1.11.