I've been looking for a place to throw this in about "random screening," since this is part of the issue here. My father worked for an IT company that assisted airlines. He was part of the team that wrote CAPPS, the system that "randomly" selects passengers. According to him, the way they wrote this system is to assign a numerical value to every passenger. There are certain things you can do to trigger a higher number value--the one I remember off the top of my head is if you purchase a one-way ticket on a short notice. The passengers that get selected for additional screening are those who have sufficiently high numbers.

So it may have something to do with your flight habits if you keep getting randomly selected.