When a teacher adds a resource of the type "text page", he has choice of four formats (Form entry "Formating" has choices: Moodle auto, Plain text, Wiki-like, Markdown). However, the associated help-text (popup) has five choices: the previous four and html-format.
I would guess that a html-format was available in that context in a previous version and the help-text is out of date. Resources have gone through extensive changes and the html-format is now available as its own type (web page).
Am I correct? Is this a known issue? Should I make a bug report?