Why is the Ampersand usage in Microsoft Office Spell Checker non-consistant?

For example these are valid:
John &Doe
John& Doe
John & Doe

but this is not
John&Doe

Why is it when there is a word on either side that the red squiggles get kick off?

How about these?

Valid:
The& - &The
A& - &A
M&R - A & B

Invalid:
And&And

In some cases it is valid. For example when talking about gatherings like gala balls as in "The B&S Ball" (Bachelors & Spinsters). The bottom line is that I'm not sure why even having the ampersand next to a word is valid, but if it is a bug or by design; please explain?