Cal already explained how it works, you need a high level building to benefit from the unit production cheat.
Example
Level 1: 1,2,3,4,5,6,7,8,9,10 normal right
Level 2: 1,1,2,2,3,3,4,4,5,5
Level 3: 1,1,1,2,2,2,3,3,3,4
and so on...
Lets say your building has leveled up while you have units queued, then you need to remove them, go to construction and then clear your mouse from any highlights, then push 4 and quickly swap to recruitment to requeue.
If you see wierd numbers jump like this
1,1,1,2,2,2,4,4,6
That means you havent been fast enough, remove the gap and beyond then start again.
1,1,1,2,2,2,3,3,3....
[Edited by sauced, 3/5/2009 8:00:57 AM]
[Edited by sauced, 3/5/2009 8:27:01 AM]