"The dirty jacket is mine."
Translation:Den skitne jakken er min.
I believe it's because when using adjectives in the definite case, you change the adjective to its plural form ("rød bil" becomes "den røde bilen"), meaning "skitne" would have to be the plural form of "skitten" (keep in mind im not a native speaker and i might be wrong about this)
Hmmm... an interesting theory, which would actually explain how it comes to be "skitne" here and not "skittene". The "Tips and Notes" section merely says that for the definite form, you (in general) add an "e" to the adjective. They don't say anything about using the plural form of the adjective (which happens to be that same rule: add an 'e'). After re-reading the "Tips and Notes", I can only say that the section on the "Definite Form" is poorly described. Perhaps you are right though; maybe the real rule-of-thumb is to use the plural form for the definite case.
I think the hover-over audio is automated for many, if not all words. "den" sounds like "dn" at the end of words like hunden, so the algorithm seems to be using that rule for the word "den" as well. I reported it about 5 times, but I think whoever recorded the voice might be long gone.