DaveC,
The old age is catching up to you my friend!
I have noticed that the test light will come on as soon as you get in the infared beam, and then will shut off. I am not exactly sure why it shuts off, it could be that it has some charge delay or something. My Moultie Game Cam II from last year was MUCH worse at it. If you set the test light off, you had to entirely move out of the area, wait about a minute, then go back up and try again. The stealth will turn on, then turn off (could be a way of saving battery life), but within seconds will be ready to go off again.
One more thing though, I noticed that if you are directly in the center of the infared censor, the test light won' t go off.