A click but no ad unit impression

Could this be a cookie?

[peewhy]

I've just noticed in my display report that I have been credited for a click but without an ad impression.

Is there a logical reason for this?

[lammert]

The statistics for impressions and clicks are not updated synchronously, so it is possible that you see clicks in your statistics without impressions. My record high is three clicks on one ad impression. My CPM was $820 :) at that moment. Unfortunately statistics and CPM returned to normal soon after :(

[peewhy]

Its strange because it now shows 2 impressions 1 click, 200% ad unit CTR and an eCTR of $950.

I'll monitor with curiosity.