Have you used tester on another PSU to see what it does? I have not used a tester to short it would make sense if after a certain amount of time it does power off.
Are you sure you are making contact to both pins when shorting? First check spot as it could be bad if not in correct holes. But if you make contact it should be the same as if a switch is used.
Yea, that was my original thought until I tried one of my Corsair psu's with it, and it worked perfectly. The Corsair PSU in my original post is running with another identical PSU tester.
Tester's are a standard for shorting PSU's to use with miner's. You can see them in a lot of the pictures of big farms. Mainly cause you can get them for 2-3 bucks. If a psu tester turned off after a short amount of time it would defeat the purpose of the psu tester. It would also require more logic, and therefore more cost, and therefore a smaller fiscal bottom line.