If a mkv/mka file do not contain any metadata tag, then foobar would display chapter names contained in chapter atoms. But foobar would not display album name or artist name, as the file do not contain any metadata tag.
In another case, if a mkv/mka file contains metadata tag (eg. album name or album artist field), foobar would try to look up title field for each chapter in the metadata tag. If a chapter do not have a corresponding title field in metadata tag, foobar would not consider the chapter name in chapter atom and assume it to be empty title.
I hope foobar developer would fix this bug. Or masstagger developer would make copying chapter name to tag field possible.
Can you check if foobar2000 1.6.6 beta 1 improves what you're describing?
Oh my god, welcome back to the fold, Florian!
foobar2000 1.6.6 beta 4 display chapter names correctly.
Thank you for the improvement!