I tried to get bee nests from trees created by sapling. I managed to get some, but bees never get out of them. I picked them with silk touch, there is written "2 NBT tags", so I assume that there are 2 bees in there, but they never get out (it is day, and the weather is clear)

There is no block in front of the bee nest, everything should work fine.

(I precise that I am on a vanilla server)