Derivational morphology allows for the creation of new lexemes through affixes, often altering the grammatical category or the semantic meaning of the base word. Analyze the following morphological constructions regarding their semantic and grammatical correctness:

I. The prefix "un-" in "undo" indicates reversal of an action, whereas in "unhappy" it indicates simple negation.
II. The suffix "-en" in words like "widen" and "shorten" functions to convert adjectives into verbs (causative meaning).
III. The prefix "mis-" in "misunderstand" adds a pejorative meaning or indicates an action done incorrectly.

It is correct what is stated