If you create offline assignment (mod_assign) there is an enabled dropdown "submission comments" that does not make any effect because submission comments do not work for offline assignment.

In order to not confuse a user we need to either disable dropdown or make comments work.

(12:05:58) Damyon: Hi Marina - that would be a separate issue (and a tricky one to solve). The submission comments do not appear until a submission has been made (because they need a submission id). To disable this setting in edit for would need a "disabledIf all other submission plugins are disabled"
(12:06:21) Damyon: But you can log a bug for it