+1 not being able to link to headers on long READMEs is very frustrating. I'm surprised the parser can't just create an id for headers. This issue needs to be re-opened. I'd commit a patch to make this work if it knew where to or even if I could?
Yes, John is right on! This cannot be considered true markdown as long as the consumer must know internal implementation details of bitbucket's parser. The purpose of MarkDown/CommonMark is to be universal! Continuing on the stubborn path of keeping the link generation logic unique just fractures the community.