When you have Tabs on a window, each Tab will print to a separate detail area (which leads to a different page per Tab if you set the Detail with the page after attribute). On a window with tabs you may have controls on the window, outside the Tabs, that you always see no matter what tab you select. In a way, those controls "on the window" are repeated for each Tab, as you can see them for each Tab you select.
When you generate the printout, you have an option.
The default for "Controls on Window" is "All pages". The controls on this particular window will be printed on each page with each Tab, so when you see each page alone it looks exactly like what you see on the window when you select that tab.
You may select "First page only" if you want to print those controls only in the first page, with the first tab. This could be a good option if you have the Tabs below the fixed information and don't jump pages on Tab change, so you see the fixed information and below, each Tab in sequence.
You may select "Last page only" if you want to print those controls only in the last page, with the last tab. This could be a good option if you have the Tabs above the fixed information and don't jump pages on Tab change, so you see the Tabs in sequence and below the last of them, the fixed information.
This option will be activated only if you tick the "Override globals" setting.