Troutman - I went down and read the label on my bottle of T17. The label does say that it has a rust inhibitor added. This may be the residue you are seeing if you are not drying the bore and using gun oil.
I have found that T17 is an excellent cleaner for BP and its substitutes. My history with it was to use it initially at the range before coming home, then after a hot water bath and rinse to be sure all fouling was removed. I then dried the bore thoroughly with alcohol patches and dry patches the a light coat of gun oil while the barrel was still hot.