1script - 4:18 pm on Jan 30, 2013 (gmt 0)
As the graphs get updated in WMT, I am now seeing more sites starting to show this spike of impressions not followed (or going in opposite direction) by clicks. I now strongly believe that they've just messed with the math behind the impression calculation or simply changed the definition of what an impression (at least the one shown on the graph) is.
It's Google's version of cooking books - practically harmless and costs nothing but may make you feel a bit better about them because they show your links more often yet slightly embarrassed to complain about anything else (Google Images, for example) because your CTR is so dismal. I am sorry if this comes through as paranoid, I find myself to be unable to think positive about Google intention anymore these days.