dhtmlcombo not display correctly in IE8

I use dojox.layout.ContentPane to create 2 tabs (ex: tab1 and tab2)
tab 1 and tab 2 are two pages which have at least one input.

I use dhtmlXComboFromSelect to convert input into dhtmlxcombo (readonly mode).
In tab 1, I choose tab 2 and then, back to tab 1, the dhtmlxcombo in tab 2 does not display.
It works fine in IE6, IE7 and Fire fox, except IE8. I use dhtmlxcombo v2.5

Please give me advice. Thanks.

Does the problem occur if the combo is not in tabbar ? We need the complete sample to recreate the issue locally