You've got a float level issue or a fuel inlet valve issue or no issue.

The same tube that drains fuel from the carb when you open the drain is often used with a standpipe inside the bowl to drain off overflow. It is very common to see fuel dripping from vent tubes when the trail is challenging. The fuel bowl is jostled and tipped just as the bike is and when there is a standpipe in the bowl, fuel is allowed to come out pretty often.

Folks that have not seen this have just not ridden hard enough. Don't expect no fuel to leak, but you also don't want it pouring out.

 

True! As long as you are not running rich, and fuel isn't *pouring* out of the overflow. I don't think it's much to worry about.
I find traces of fuel in the overflow line when I have been off road, or when the bike's been parked in the sun.