It happened all the time on my old Yamaha WR400 when I let it idle. I never liked the idea of it glowing, so I tried not to idle very long. But in my opinion it is pretty normal on big bore four strokes.
I think a lot of people don't notice that their thumpers are glowing red because they seldom ride at night. The glow can be seen in daylight but obviously not as easy as in the dark.