tedster - 6:09 am on Jan 21, 2012 (gmt 0)
There's only one thing I've read that might be relevant, and I'm not sure it's relevant to your situation. Google does maintain three different sets of "mobile" results - one each for feature phones, smartphones and tablets.
However, those are very big swings in the numbers you're seeiong. Does make you wonder what's going on.