This is a pretty weird problem. I have done a bit of debugging into it, which hasn't proved fruitful, but did allow me to rule out a few things.
So, starting it off... I see this when I drill on a Microsoft Chart Control hosted as content in a RadDock, BUT I only see it on IE (Tested IE 9.0.8112).
The ImageMap for the chart renders to the screen for a second upon clicking of the chart.
Here's a pastebin for the imagemap mark-up. Sorry it's not well-spaced..IE slaughtered it. http://pastebin.com/3bdxbcC4
Once again, I don't see this issue in any other modern browser. In addition, I moved my chart control to a separate solution, mocked up a couple of data points, and did not see the image map rendered. This is NOT to say that there is conclusive evidence that the issue is on Telerik's side, clearly I could have introduced/removed the issue in another part of my solution, but I am not sure and do not have much debugging information to go on.
As such, has Telerik experienced this sort of issue in the past? I didn't see any users mention it, but I suspect everyone's using the Telerik Chart Control.