Removing last group doesn't give the player default permissions back

I just had some players complaining about not having permissions so I checked my permissions file and found a lot of user in there without any specific groups/perms. They look like this:

users:9eae5adc-7995-4382-a56c-fb11a0862dd7:groups:[]name:recon_

Steps to reproduce:

• Create 2 groups (default and let's say 'special')
• Do not write any users to the file by hand. Just the 2 groups.
• Execute /permissions player addgroup <name> special
  

The user should now be written to the permissions file with the group 'special' assigned.

• Execute /permissions player removegroup <name> special
  

Now the player's entry looks like the example above. If you now reload the perms and/or relog, the player doesn't have the default group.
In my opinioin the player should get completly removed from the file if the last group gets removed from him.