There is indeed something strange about this.
I have OWC Mercury Elite AL Pro QX2 raid drive attached via eSATA to an OWC eSATA card on my Mac Pro.
This never has an issue.
I also have a OWC Mercury Elite AL Pro drive with USB/eSATA/FW drive.
When this drive is connected via eSATA to the same OWC eSATA card on my Mac Pro, I always get this problem.
When this same drive is connected via USB or FW I never get this problem.
Swapping ports and cables to the OWC eSATA card - no change.
OWC sent a new drive - no change.
Swapping ports and cables to the OWC eSATA card - no change with new drive.
OWC says that htey couldn't reproduce on the returned drive - though I'm not 1000% sure they had exact same configuration. (And I think it is some precise combination of things that casue this problem)
They now think it might be the OWC eSATA card - which makes no sense to me. I suspect that there is something quite specific in configuration that exposes something in the the eSATA firmware in the drive that causes the drive and OS X reveal this problem.
I've just defaulted to FW800 on the drive as it only now used for backups and the lack of eSATA doesn't thrill me - I paid for it - but it doesn't impact my current operation.