"Step foot"?

Like most college professors, I am now grading many papers. And this brings up all sorts of grammar and usage-related questions and leads me to ask again what is being taught these days? One of the new phrases I'm finding is this:

"from the time the first settlers step foot on the continent..."

Step foot? Where did this come from? And why are teachers not correcting this? It's set foot.

One can either step, or one can set foot, but it makes no sense to say that one steps foot. I am mystified where these things come from, why they take hold, and why they're not strangled immediately by teachers.

Here's another one that amazes me. "He lead the miners to the lead mine."

Is no one correcting the incorrect spelling of the past tense of the verb "to lead"? I see this a lot.  It's led.

And why does everyone these days write dates incorrectly? It's not December 17th, 2011. It's December 17, 2011. I even see college administrators do this frequently. It looks so silly with that ordinal hovering over the comma. That alone should let people know that it's not correct.

And permit me one more: there's no such word as alright.  It's two words: all right.


All right, enough from me.