Null tabs appear on IE

We are using the tabbar in our application and it seemed fine until recently.

We noticed that in IE the tabbar suddenly started showing null tabs between every regular tab:

| null || TItle 1 || null || Title2 |

We are using tabs defined using Divs ( classes dhtmlxTabBar and tab ).

Even the simplest of tabs (no javascript) now have this problem.

The problem only occurs on IE, not FireFox.

We see no javascript errors.

It must be something in the environment which has changed, but we cannot figure out what.

Do you have some suggestions on what can cause this or how we can diagnose the problem?

Problem caused by HTML comments or any other unnecessary tag inside tabbar container.
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