Bitbucket issues and issue comments and rendered as Markdown. However, prior to Oct 4th 2012 everything was Creole. Bitbucket still applies Markup based on the issue's timestamp so that old content continues to render in Creole.

However, when converting content from an external, Markdown-only issue tracker to Bitbucket, anything with a timestamp prior to Oct 4th 2012 incorrectly gets rendered as Creole.

So issue exports should be extended to contain the actual markup language for the content. This requires a database change on our end, as this data is not currently tracked.