AFAICT, without a commercial licence the way to raise a bug report is to mention it here so Atlassian can vet it and raise the report itself if appropriate.
In Bitbucket's on-line tutorial Getting Started, the Git Reset page has a subsection 'Staging index'.
The third paragraph includes, "Here we are interested in the object name, the second value (d7d77c1b04b5edd5acfc85de0b592449e5303770)." That SHA1 hash is wrong:
- It doesn't match "the second value" shown in the screenshot
- It doesn't apply until later in the subsection, after the change has been staged.
The correct hash at this point - from the first screenshot in the subsection - should be e69de29bb2d1d6434b8b29ae775ad8c2e48c5391.