It is a little complicated, but bear with me: Swedish language uses the very same letters for the English word 'under'. Here comes the twist: unfortunately the letters are in the same order as in in the English 'under'. It is tricky - I know - but with a few years of practice and perhaps living in Sweden for several years can help you get it down to some extent.
We're currently in an A/B test so I can't know for sure which voice you're hearing, and I can only hear one of them myself, but I think they both say this correctly. It's a sound you don't have in English and it sounds nothing like the English 'under'. Hear a native speaker say it: http://sv.forvo.com/search-sv/under/
Swedish has more different vowel sounds than English.
Edit: the A/B test has ended and the new voice definitely says this correctly.
I hear only a small difference between the Swedish vowel sound in the first syllable of 'under' and the English vowel sound in 'put'. Also, in certain British accents (e.g. Yorkshire accents) many more words contain that sort of 'u'. The Forvo English pronunciation of 'under' by TristanJaimes, for instance, isn't so very far from Swedish, is it? Am I just not tuned in to the subtleties of Swedish vowels yet?
I'm sure the sound exists in some English dialects, you can also hear it in Japanese for instance. To be more exact I guess I should have written that this sound is not a phoneme in Standard English.
The sound that most speakers would use in put however would be another vowel phoneme in Swedish, which would usually be written with the letter o. (o can sound in two ways, either like that or in the same way that the vowel written as an å sounds.)
It's not that "my" means "min" and "mina" means "mine". Min/mitt/mina can all mean either "my" or "mine", you must just have run into different forms in different contexts.
- Det är min hund. / Hunden är min. - It is my dog. / The dog is mine.
- Det är mitt hus. / Huset är mitt. - It is my house. / The house is mine.
- Det är mina skor. / Skorna är mina. - They are my shoes. - The shoes are mine.
I'm assuming you mean "under your spell" as in a magic spell, and I'm afraid that phrase doesn't really work for two reasons. First, "stavning" means spelling in the grammatical sense. You spell a word right. Du stavar ett ord rätt. A magic spell is a "trollformel" or "magisk formel". Second, the phrase "under your spell" as a whole doesn't really translate literally to Swedish. I would recommend for example "Du har förtrollat mig". "You have enchanted me".
It does work with befäl/command, however. That part was right.