This is something I don't understand and can't find in the documentation. Suddenly when I am sketching and adding dimensions some of the dimensions will automatically have an equations attached to it. I don't understand what the difference is between when it happens and when it does not. I am wondering if I accidentally activated a preference with a hot key? Has anybody else seen this and understand why it happens?
That had happened to me in the following case: There had been a dimension in the part with an equation linked to it (let's call it D2@Sketch1), and that dimension was deleted or renamed. Now I add a new dimension which receives the first available dimension label, and if that's D2@Sketch1, it automatically controls your dimension with the equation.
So if this is your problem, go edit your equations list and delete any equation that are not supposed to be used. And if you ever delete a dimension that was driven by equation, be sure to go delete that equation too.