It sounds like anb object behind the nav bar has a link applied to it which when moused over causes all the mouse over states of the nav bar to be displayed.
Hold Ctrl and select individual objects behind the nav bar whilst the Web Properties window is open on the Link tab. When you find the object which has a link applied select the Do Nothing option in Web Properties and click Apply.
This will more than likely need to be done to all of the pages in your site that this effects, so it's worth previewing each page to see what ones need to be updated like this.
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