Well, yes, then it must have been a glitch. When such things happen, make sure you take a screenshot, upload it somewhere (like Google Drive, for instance), and then report it and explain what happened, pasting the link so the developers can see the screenshot.
My question too. 'Pants' signifies a single item of clothing although it 'sounds like' a plural. Hence saying 'my pants is' is acceptable, while saying 'my pants are' could mean more than a single (pair of) pants. It's not simply American or English - it's almost universal and 'a pants is' should be accepted as an answer.
Well, "Draag" is when you're talking about yourself. "Draagt" is when you're talking about someone or something else in the singular. So ik draag, zij draagt (she), zij draagen (they) (plural), hij draagt, [noun] draagt, and so on and so forth. Also, the add-a-t rule works for most other verbs, such as spreek/spreekt, drink/drinkt, etc.
Because Dragen is what we call the infinitive. So for first person - ik: the general rule is to remove -en to bring it back to the 'stem' and then you add another vowel to keep the sound in the open syllable long so now it would be draag.
for second person - je, u, jij & third person - hij, zij, het: you add a 't' to the stem -> so draag + t = draagt
for plural - jullie, wij, zij, ze, we: you take it back to the infinitive -> dragen.
Therefore, if the sentence were in English "the mice are wearing pants" you would use dragen because it is plural and that goes back to the infinitive verb. "De muizen zijn dragen broeken"
In Dutch, "een broek" is a specific pair of trousers. "Broeken" is more than one pair of trousers. So you could say that the mouse is wearing one specific pair of trousers "De muis draagt een broek". Or you could say that, perhaps due to very cold weather, the mouse is wearing more than one pair at once: "De muis draagt broeken". I think the latter could also maybe refer to habitual action: the mouse is simply in the habit of wearing pants. But anyway, that's how both can be correct I think.