<<How bothered would y'all be in this situation?>>
I think it would bother anyone if the teacher doesn't even know simple things like that.
That's the state of modern education, though. I'm sure someone will nail me for saying this, but my impression was that some of the dumbest people went into education at my college, and that could further be broken down into the dumbest of the dumb going into elementary education. That's not true in all cases, but the standards in the education college are INCREDIBLY low. The roommate of my girlfriend in college was majoring in elementary education, and she had to make poster boards and think up fun things to do with crayons. That's it, and ... I'm ... not ... kidding. I couldn't believe she got a degree; in conversations she didn't even have a dim awareness of the most basic things. I know that some smart people also go into education, but the low standards kind of drag everyone down.
Even preparation for teachers at the high-school level involves more of a focus on the psychology of learning and the like, and not much focus on knowledge and facts. So these students get out in the real world with not much knowledge to impart to their pupils, but all of the psychology of learning also goes out the window when they face reality in the classroom.
Combine that with powerful teachers' unions that actively work against the testing of teachers, affirmative action to the extent that they don't seem to CARE if teachers don't know math or spelling or English or anything else, and also affirmative action starting in the college selection of teachers, and you've got a good recipe for what you see going on.