Looks like we can't reproduce the issue or there's a problem in the test case provided.
GXT 3.0.1 grid has column alignment issue on Chrome
I have seen columns misaligned with column headers in both my application and the GXT explorer. I was thinking surely somebody else has reported it but I couldn't find it on the forum. It is easily reproducible. Just open the GXT 3.0.1 explorer and navigate to any grid (http://www.sencha.com/examples/#ExamplePlace:basicgrid) and you will see the columns misaligned. The Chrome version I used is 28.0.1500.95.
I can't reproduce this as-is at the url you've provided - at least not without using browser zoom, and for zoom in the bug only presents after refreshing the page.
If that is what you are reporting, can you verify that we fixed it along with other zoom issues at http://qa.sencha.com:8080/examples-3...lace:basicgrid ?
Assuming that is the bug you are looking for, I found it by searching 'chrome zoom grid':
According to that, it seems to be fixed in 3.0.5 and later, along with this other chrome grid zoom bug: http://www.sencha.com/forum/showthread.php?254438
Fixed in 3.0.6
Yes it is fixed in 3.0.6. Thank you very much.