Rereading the instructions for adjectives, I'm still struggling with korte vs. kort. We're taught that definite adjectives are an exception to Danish postfixing - instead the adjective declines to the plural even though the object is singular. Den korte kjole. I get that. 'Min' however, isn't a definite article; it's a pronoun. Is this sentence an exception somehow, or have I misunderstood the rule?
The possessive pronouns, min, mit, din, dit, hans, hendes, and so on, make the object definite. It is one certain item.
(Also technically that adjective form isn't the plural form, but the definite form. Those two are identical for the most part, though, with the notable exception of "small": "det lille hus" vs. "de små huse".)