5.1 inserts spend a lot of time in the "closing table" thread state

[Eric Jensen]

I'm seeing 5x slower insert performance for my application on 5.1.25 vs. 5.0.51. One big difference I can see is that instead of the "update" state that I typically catch inserts at in 5.0, I only occasionally catch 5.1 insert threads in that state, but rather most often catch them in "closing table". I'm not sure if that's just a bad description of what's happening or not, but I can see in the status that I have far fewer tables open than my max cache, table opens counter is not growing, etc. Anyone else have this experience, or any ideas what it means?

thanks,
eric