When drafting, in each and every draft pool it's immediately possible to identify cards that one will be able to pick in large numbers. In each out of 10 trial drafts I was able to pick as many as 12 copies of a single common and as many as 6-7 copies of an uncommon. The over-common cards are different from draft to draft, but they're always present. This behavior is repeatable between different expansion sets.
This seems to me like a booster generation issue.