Hi Brian,
It is a common issue. As JiMa explained it is due to the fact that either the adobe image request did not have enough time to be sent before the next webpage is loaded or the image request is ent correctly but the response was not received because the next webpage was loaded to fast.
1. With H code H.25 and above has updated the code to wait 500 ms before moving to the next page : http://microsite.omniture.com/t2/help/en_US/sc/implement/index.html#Manual_Link_Tracking_Using_Custo...
2.Another way to do it is to set up a timer to wait 500 ms before moving to next page. So send image request to adobe start timer (500 ms (I usually use 700ms)) then move to next page. The idea is that you will have to prevent the default action of the link first.
3.The third solution is to open the link in a new tab target="_blank"
Best regards.
Alexis Cazes