Perfectly normal.
A bike clutch has ~7 friction disks that are sandwiched by steel plates. With the clutch engaged, the pressure plate puts pressure on the sandwich which gives you forward drive. When you pull in the clutch lever, you are pulling the pressure plate off the sandwich. When you shift from neutral to 1st, the friction disks spin, while the steel plates stay stationary. When the bike sits, the sandwich sticks a little bit. That clunk you're feeling are the friction disks breaking free from the steel plates, as they spin while the plates don't.
Hopefully that made sense.