Hi CarolSkeller,
I don't remember ever being able to use the arrow keys to tab around an InfoPath form. Tab and Shift-Tab go forward and back but arrow-keys shouldn't have that behavior since you need them for intra-field position movement and moving out of a field will trigger any rules on that field - that's one reason why I can't imagine arrow keys every having worked in tables.
Sorry to rain on your arrow-key parade,
P