Here's the USPS announcement:

http://about.usps.com/news/national-releases/2012/pr12_114.htm

I think your postal clerk is correct. Your mailings have always been classified as a first-class package and should have been $1.95.

Here is a document with all the regulations on classifying your shipment:

http://pe.usps.com/text/dmm300/133.htm#1041530