He's putting linebreaks in. 

[center]

There's two linebreaks above this.
And below this.

[/center]

[center]
One linebreak above this.
And below this.
[/center]

[center]No linebreaks above this.
Or below this.[/center]

[center]All on one line. Works just fine.[/center]

EDIT: Whelp, interesting, that all works. Let's see if his exact code does the same thing:

[center] 

vvvvvvvvvvvvvvvvvvvvvvvvvvvv
vvvvvvvvvvvvvvvvvvvvvvvvvvvv
vvvvvvvvvvvvvvvvvvvvvvvvvvvv
vvvvvvvvvvvvvvvvvvvvvvvvvvvv

[/center]

EDIT2: Glitch fixed already? Does your QQCode evaluate on post submission or post load? If the former, it could be code that's already fixed.