Why can't I sign out of mac app store?

When I click Purchases, I see:

You must sign in to view your purchases.

I click sign in and enter my AppleID and password (which I have verified are correct by visiting My AppleID)

After a few moments of rotating chiclets, the sign in dialog drops away elegantly and I see:

You must sign in to view your purchases.

I click Store in the menu and I see:

several not relevant choices

Sign Out

View My Account (myActualAppleID@listed.here)

I click Sign Out and I am less elegantly returned to the Featured display.

then I click Purchases, I see:

You must sign in to view your purchases.

I can do these steps over and over (trust, I have.)

No bueno.