I've whipped up a quick test application to show what I'm talking about.
If you load default ASPX click on "Tab 2" (do not then click on "Tab A"), then click the checkbox. The red box will change to a checkbox as expected.
Then go ahead and click on "Tab A" to select the tab. Then uncheck the checkbox. The image will then disappear. If you then hover the mouse over the tab, the red box will appear as expected.
It will act the same for "Tab B" and "Tab C" -- if the tab is selected and the image is updated, the image will be hidden until hovered over. If the tab is not selected it will work as expected.
testapp_1714399a.zip