Acid2 is actually not a 100% standards compliance test. And it also tests non-standard error corrections. So, it is possible to pass Acid2 and still have a very buggy browser.
I looked it after, and I think it's a bug - I couldn't isolate it so I am not sure. There is so some rules to trigger the hasLayout properties in IE6 and IE7 but I don't think they have anything to do with it.
About the ie7 emulator, it does a good job but it's not perfect. There are bugs in IE8 render mode with the avatar, that are not fix with the emulator.