The bug
When you try to summon an entity with an invalid id, the message "Skipping Entity with id " will be printed in the Game Output of your launcher. However, the entity id you entered is missing.
How to reproduce
Use the following command
/summon InvalidEntityId→ "Skipping Entity with id " instead of "Skipping Entity with id InvalidEntityId" will be printed in the launcher
Is this still an issue in the most recent versions (currently that is 1.10.2, or 16w43a) of Minecraft? If so, please update the affected versions and help us keeping this ticket updated from time to time. If you are the owner/reporter of this ticket, you can modify the affected version(s) yourself.