Thanks! This kind of bug report should ideally go on the github tracker instead.
Can you try with the current dev version from jgm/cmark? I wasn’t able to reproduce the problem with that version, and I see that there have been a number of patches improving handling of tabs since the 0.24.1 release. (Perhaps another release is due soon!)
Happens also in 0.25.1
Opened in bug tracker.
Nice idea to have also cmark online, but it is maybe simpler to put on the home page the link not only to the GITHUB repository, but also to the frozen version.
Thanks!
mario