One misty, moisty mutant

My friend Nicole, traveling in Zanzibar last week, saw the label on a shipping box: the umbrella symbol and, beneath it, the not unexpected advice "Store in dry place." But the rest of the admonition was not so straightforward. It read:

AVOID MUTANT FROM THE MUSTY

 OK, "the musty" must be whatever sort of mildew or mold likes to grow on damp shipping cartons in Zanzibar. But can my multilingual friends out there hazard a guess as to what word might have given rise to "mutant"? Some synonym for "growth" perhaps? Or for "spreading"? Or for "contagion," that current financial buzzword?

And while we're on the subject, do you use mildewy and musty as synonyms for the dank smell of the fungus among us? If not, what's the difference? (Food can only be moldy, as far as I know, but I tend to waffle when choosing between the other M-words. If you have a rule, please share.)