Tab has a gap in the IE6

Hi,
I just want to do migration an app from GWT-Ext to SmartGWT, everything looks fine, but when I tried to visit my app in the IE6, I found the tab seams something wrong, there is a small gap on the tab, as the attachment shown, but it’s all right in FF and IE7, I don’t know why, according to the image in the Issure 426

They works fine. I did some test, if the title is long enough, the gap will disappear, Is there anyone got the same problem?Please advise.

I using GWT2.0.3
SmartGwt2.1 (After testing 2.2 has the same problem.)

Thanks.

My screen shot is in the attachment.

addition

I used some IE6 simulation tool to simulate the IE6 environment, could this is a possible reason?