It is currently impossible to submit a new release with a tracklist containing fullwidth spaces (specifically U+3000 IDEOGRAPHIC SPACE but I assume other types of whitespace behave similarly), as they are automatically converted to ordinary spaces.

However, some older releases still contain such characters in their tracklists.

If that needs to be changed, that currently seems to be impossible to do with the release editor. If you edit only the whitespace (e.g., replacing a fullwidth space with a regular one) and try to submit, the release editor simply says "You haven’t made any changes!" which is simply not true, and it does not allow submission ("Enter Edit" is grayed out on the interface).

However, if you make a totally unrelated non-whitespace change to a track the whitespace will be automatically fixed for that track. So there is a relatively easy workaround if it is possible to make an unrelated auto-edit (and then reverse that change) but it should be possible to fix whitespace without submitting bogus edits, especially as it may not always be possible to auto-edit a bogus edit into place depending on the track title...

(For example: I was able to adjust this for one particular release via edit #70676042 - edit medium followed by edit #70676046 - edit medium)