I was thinking the same. Spanish and English really share a lot of little quirks like this. In other north Germanic languages we certainly wouldn't use the word for "under" to express someone being in a state of arrest or whatever.
Would Spanish also use "bajo" for expressing something like "driving under the influence"?
In a lot of places, the use of usted is incredibly rare in any circumstance. I've actually been told a few times that using usted feels like there's some sort of barrier between the two people...sort of overly formal. While I could certainly see a police officer using usted with that in mind, I can also definitely see them using tú form.
I was wondering the same thing. I'm not sure about Spanish speaking countries, but I've heard that in France it is extremely offensive if a police officer "tutoys" you (esp if you're from an ethnic minority). "Tu" can be friendly but it's also how you address children, dogs and servants.
It's easier if you forget about the permanent-temporary thing when deciding between ser and estar. Estar is used when talking about the state of something/someone, as in you're 'in a state of being arrested'. Being an actor is talking about a profession, and profession uses ser. Basically, the temporary-permanent guideline only works for state of being and/or opinion, but ser is used for characteristic. For ex:
• La manzana es verde = the apple is green --> characteristic/color.
• La manzana está verde = the apple is green [meaning unripe] --> state
• Eres feliz = You're a happy person --> characteristic
• Estás felíz (hoy) = You're happy (today) --> state