If you can see Adwords at the bottom and top of your SERPS (not all browsers can yet), then mouse over the text in the blue area at the bottom, you can see that it should take you to the URL link shown directly at the left, but it takes you to the respective Adwords URL displayed at the top of the screen.
Click on the URL link itself, and it is correct. The problem is only with the text in the blue area of the Adwords box.
For example, Google "click fraud detection" and there are two (or three) Adwords at the top of SERPS, and two at the bottom of the page (in a blue shaded box). Mouse over the text to the right of the link at the bottom, and you will be taken to a site listed in the blue Adwords box at the top of the screen instead.
I just checked my PC for spyware to make sure it wasn’t being hijacked, but it's clean. Anybody else seeing this bug?