Weird kicking while sitting?

Okay. I go on my Bukkit 1.6.2 (dev build) server, and right click a stair. I'm sitting! That is cool, but when I dismount (Left shift key) I get kicked and then my minecraft client crashes. How did that happen? Did a plugin cause it? How do I fix it?
In the console, this shows up:

When I right click a stair it also says:

When I try to break it, it says

This is the list of plugins I have if that would help:

Anyone else got this glitch? I don't think this is on Bukkit's side, it may be one of the plugins.

 

Delete anti-grief and see if the error continues.

 

Same thing.

 

Had the same, craftbook causes it.

 

CraftBook doesn't cause it. It's completely a bug in bukkit and has nothing to do with CraftBook.

Use bukkit build #2812 to fix the issue.

 

I fixed it by turning chairs of craftbook off.

 

It's a bug in bukkit that happens when you dismount a non-vanilla rideable mob. Craftbook puts you on an arrow, craftbook doesn't cause the kick, bukkit does. Using bukkit build #2812 fixes it.

 

Thanks everyone!

 

So basically disable chairs or use bukkit #2812. But it's weird you only noticed chairs now, they've been there for a year