You might want to check to make sure everything's tight. I believe doing a hot restrike is usually pretty hard on an HID system. Once you turn them off, you're supposed to wait for them to cool before you turn them on again. Some of them have a hot-restrike capability, I guess, but I haven't done the full research on it.
Anyway, what I'm getting at, is make sure you don't have a short or break that could be causing the light to flicker out.