I've had this happen twice in the last year at JFK T4 only. going through with my boyfriend once and my sister and 2 friends another time, all on the same PNR.
The Delta rep at the front of the SP line said only I could go through, all others had to go through the regular line, I explained we were all travelling together and insisted this was okay, each time the SP line had 2 other people in front of us at the TSA agent, the other line was zig-zagging.
She - the Delta rep - let me go through, both times stating that the TSA agent would just send the rest of my party back.
Each time the TSA agent let us all through with no problems/questions.
This has only happened twice with my travels through JFK T4, but has never happened anywhere else.