2001 expedition bypass

just ran into an odd problem with a 2001 expedition,  I programmed my transponder box ( pats 1) using key 1 then 2 then pats box....... then tested the starter ant it worked fine,  tested it a few times  times with no problem.

a short time later the bypass  would not work,  the keys would work... I even went as far as to take out the transponder from the box and hold it close to the tumbler,  ... the vehicle seemed to have rejected the transponder, I cut one transponder out of one of the keys and put it in the box ...and it works fine, just on a hunch I put the pats 1 transponder into the key I emptied out and now it works again,   looks like it temporarily rejected the pats transponder (15 min.) any thoughts ? anyone ?