Known issue? SF U2 shuts down after a few minutes

I bought a U2 on the B/S/T section a few months ago. In the beginning, it was working fine, but now, it shuts down after a minute or so on high. On level 4 & 5, it works a bit longer, but after a few minutes, I have the same problem.:mecry:
First, I thought there was a problem with my cheap ultrafire protected 18650's, but now I have a new set of (also cheap) smartfires, and my light still shuts down. I have tested it now with primaries and also with a regulated power supply, with the same result. Is it a thermal problem or so?
I live in Belgium, must I send the light to the states for repair?

i wouldn't think it would be a thermal problem if it shuts off in a few minutes, mine barely gets warm in a few minutes.
unless it's not heatsinked properly.
and it's normal for it to shut off like that.

Sounds like it might be time to try out SF's best-in-class warranty service.