TSA and CBP are two different organizations. TSA processes you from land to air side at an airport security screening point while CBP processes you back into the USA.
I found this out when I asked if I could do the advanced clearance thru security since I was Global Entry and the (annoyed) TSA guard told me "We do things differently." He then (gruffly) explained that the airline has to process it and that TSA then has their own checking process.