Master Sergeant in his 80s.  Receives monthly check from DFAC.  Tax withheld, but all of it refunded.  Not thinking, I fill out a W-4P in February and mail it for him.  I know, old soldiers never retire, they are always subject to recall so they can't remind others not to obey illegal orders.  In April they send it back and tell him it requires a W-4.  So I fill that out, he makes another trip to the office to sign it, I check the "Exempt" box.  Now they have sent that one back, saying he should not have filled out marital status.  (He's married; she has no income.).  Sure enough, the W-4 instructions say to fill out just name and SSN.  

I give up.  We'll try again next year.  And maybe avoid the Exempt box, so a new one doesn't have to be filed every year.  Live and learn.  Thank you for your service.