1 - New form
2 - Four controls(any) on form - Two at top of form, some space, two at bottom
3 - Automatic Control Focus is OFF
4 - Tab order - Top Left = 1; Top Right = 2; Bottom Left = 3; Bottom Right = 4
5 - Reduce size of Form so only top two controls are visible.
6 - Run Form
7 - Select upper left control
8 - Using TAB key will only cycle through the top two controls
9 - Scroll down on the form so the bottom two Controls are visible
10 - TAB key will now cycle through all four controls.

Same as above but with Automatic Control Focus ON

FIRST TIME ONLY running the Form - 
   Will cycle through top controls until lower controls visible

Any subsequent running of this form (Automatic Focus ON) will cycle through ALL controls visible or not.