Auto fill criteria/questions on filling formulas down

I am aware of all the basic features of the fill handle- filling down, auto fill, dragging, absolute/relative references, etc.

My question refers to what happens when I double-click on the fill handle. Typically, it fills the formula down until the bottom of my table (this is what I WANT to happen).

Every now and then, in different workbooks, I will double-click the fill handle and it will behave differently. Sometimes it will fill a few cells down, sometimes it will do nothing at all. I want it to fill to the bottom of my table every time so that I can make a macro for it (as I have done with other templates that I use).

Why won't the fill handle behave the same way? Does it have to do with the column headings? None of my neighboring cells have anything strange in them (not even any functions), and all the cells that I want to fill to are blank.

I've tried searching the online help files, but there is no information about this phenomenon- anyone know anything about this???!

Thanks!