Hi Alois,
If it's normal, I really don't know. But I have the same thing with my camera lenses when moving from a cold place to warm place. For lenses this isn't really a problem, you just need to wait untill the condensation goes away.
In your case it means that the
Suunto isn't air/water tight. You can always do the test in a glass of water. If the interior of your watch stays drie, ok, otherwise you have a problem and I would return it