What's truly odd is the only way you will see placement targeting results for link units is if you have custom channels on those units. If you just run a report specifying link units only you will not see any placement targeting results (I believe anyway).

So I think it may be a Google accounting problem. Perhaps from Ad impressions from the cache?

The Link Units radio button actually disables the ability to see placement targeting. So again I believe you must be seeing the anomaly through your custom channels dedicated to link units ? I've seen the same and can't explain it.

I have some sites that ONLY have ad links on them, no ad blocks, and I recently have started seeing CPM / placement revenue in AdSense. So I'm pretty sure it's happening, just not entirely sure how.

Theory:

Maybe advertisiers can place a brand name related to the topic in an AdLink block.

Maybe on a site about blue widgets appears in the AdLink the brand name of a blue widget manufactuer.

That's been going on for a long time on my site.

I'm not sure, but I kind of assumed placement ads showed up on link units pages when the regular adblock was already taken by another placement ad.