itybitybob,
I ran into the same problem on a trip to Jamaica last year. i flew out of Dallas (DFW) airport with the small CPAP in my carry on bag. When through security at DFW with no problem. Flew back from Jamaica and went through Jamaica customs and security, again, no problem. Landed in the US at Charlotte, NC airport, and went through US customs with no problem and transferred my checked bag through to DFW. When I went through Charlotte customs, I had to do the same thing you did....send the CPAP through by its self. It went through the x-ray and when it came out the other end, the TSA supervisor said it was a CPAP, and picked it up, and carried it back to the front of the xray line, took it out of the carry pouch and then told me that it had to go through the xray by itself?? He knew what it was, and it had gone through the xray, but I guess with all the other stuff in my carry on bag, it was difficult for them to see exactly what it was?
...Rich