I am trying to put a datum tag on a diameter dimension where the cylinder is in plane view. Seems like this should be a simple task... but what I get is this:

What in god's name is that? I am selecting the dimension first, then the datum feature from annotations...

I did figure out that if I DON'T select the dimension first, then it will allow me to select the cylinder surface, and then it places like what I would like, BUT it isn't aligned with the diameter dimension. If I move the diameter dimension, the datum tag does NOT move with it...

thanks...