TabSheet in TabSheet and style problem

Vaadin 6 / 7 / 8 Framework UI
1

Hello,

I have TabSheet in TabSheet in Vaadin v7.1.10:

TabSheet innerTabSheet = new TabSheet();
innerTabSheet.addTab(new Panel(), "tab 1");
innerTabSheet.addTab(new Panel(), "tab 2");

TabSheet mainTabSheet = new TabSheet ();
mainTabSheet.setStyleName("main-tab-style");
mainTabSheet.addTab(innerTabSheet, "InnerTab");
mainTabSheet.addTab(new Panel(), "Other tab");

and style:

v-tabsheet-main-tab-style {
     ...
}

My problem is innerTabSheet has the same style (“main-tab-style”) as mainTabSheet.

Why?
 I set “main-tab-style” to mainTabSheet only.