(1) At my local P.O., one of the clerks continually tells me that a bubble mailer is not thick enough to get Delivery Confirmation. Every other clerk in the same P.O. takes them with confirmation without a problem.

Tell this person to get that peice of cardboard out ( with slit ) and see if it goes through it - Your 1st class envelope has to be 3/4" thick or better - ( Put a wad of paper in it to make it thicker ) - if he/she does it again, ask to see the Postmaster and show him the package and tell him to inform the employee that you are correct as per regulation.