Looks like we can't reproduce the issue or there's a problem in the test case provided.
Interestingly, I am _not_ able to reproduce this issue at http://sencha.com/examples-dev/#Exam...buttonaligning on an XP machine running IE7. This is a VirtualBox VM, made from an old XP cd, installed as if on a real machine.
IE Version: 7.0.5730.13
Windows Version: 5.1.2600 Service Pack 2 Build 2600
I've tested on a physical, non-VM machine, and it seems that the combination of XP with either IE7 and IE8 work without issue. I'll keep an eye out for any other configurations of Windows+IE that become available, but for the moment, I'm not able to debug this problem. If this turns out to be a more widespread issue, I'll try to collect more data from you and others to see if I can work out some correlation. Until then, please let us know if you see anything else that might help us start to replicate the issue here.
I've taken a closer look at this issue, and I've committed a potential fix. Please continue any discussion in https://www.sencha.com/forum/showthread.php?t=205452. Unfortunately, because I'm not able to test here, I can't be confident that this resolves the issue completely.