"ACL found but not expected" on running "repair permissions." ***?

When I try to repair disk permissions with Disk Utility I get hundreds of entries saying something called "ACL" was found but not expected in a whole lot of places. I assume this has nothing to do with anterior cruciate ligaments lurking in my system. The Disk Utility "repairs" these, but the next time I run Repair Permissions, they're all back.

Is there some way to fix this permanently, and does it ential any risk?