Have you checked that the macro is actually being fired on the shift-tab?

Yes, the Entry Macro is firing. I think the problem is that when you press
Shift-Tab, the Shift key is depressed, and then SendKeys fires, and I THINK
the computer is seeing Shift-Alt-Down, instead of just Alt-Down. This
keystroke simply moves you to the next field, and since Shift-Tab moves you
to the previous field, that's why I don't see ANY effect, because the two
keystrokes are canceling each other out!

I did find out that Up and Down move you just as nicely from field  to field
as Tab and Shift-Tab, and they don't have this problem (since you're not
using the Shift key), so I don't feel so bad if the user can't hit Shift-Tab
-- I'll just tell them to use Up.

So thanks -- you helped me look into it deeper and find my workaround.

This could well be the cause. I've never looked for it, but presumably there's
a function that allows you to read the keyboard scan codes from VBA. You could
put the code into a hard loop waiting until the shift key was released before
doing your SendKeys.