In Wheelock, on page 220, it says "in the following table, adverbs that do not follow the standard rules for forming adverbs from adjectives are highlighted". But male is highlighted, implying that it is an irregular formation from malus. But it seem to follow the rules to me: add -e to the stem mal-.
I can see the irregularities in all the other highlighted forms, - is the highlighting simply reminding readers that these are irregular adjectives?
or is it a misprint, or have I missed something (again!)?