I have the same - three queues of 12 unbuffed, hall shows 18 per queue(using petite cake), only 36 delivered.
Closer examination shows this:
Prod queue 1: Wheels. Base 12, buffed with petite cake shows expected delivery of 18 - delivered 18, total in house: 18
Prod queue 2: Wheels. Base 12, buffed with petite cake shows expected delivery of 18 - delivered 6, total in house: 24
Prod queue 2: Wheels. Base 12, buffed with petite cake shows expected delivery of 18 - delivered 18, total in house: 42