When I draw a simple curve with the pen tool, even if I have made each previous point a "corner" point, I get this result.
The red curve is the actual pen tool path and the black is the stroke. This is bizarre and I've never run into this issue before.
I eventually determined the problem: I had started with a box, used Style -> Round Corners to add round corners to it, and then started slicing and dicing one side to achieve the shape I wanted without using Object->Expand Appearance first. Once I used Expand Appearance, I was able to make changes to the path without the unexpected behavior.
