This almost looks like a bug to me, but I'm submitting it as as an improvement, albeit a much needed one.

In the view (non-edit) mode the feedback field of Gradebook's Single views displays plain text, which usually looks bad, since this feedback text often comes from activities such as assignment where HTML formatting is applied.

The issue affects BOTH the VIEW BY "Grade items" and VIEW BY "Users".

Both types of the Single view should display formatted HTML (as does Gradebook's "User reports"):

(I would actually claim that also in the Edit mode Single views could respect HTML, and only suitably switch to HTML editing on selecting the Override option. Cf. this new proposal for adapting the modal popup links used in the Grader report in the Edit mode: MDL-85054 .)