Postal Service Pettiness

According to my Quicken program, it was on March 5, 2011 that I purchased a roll of a hundred forever (currently 44 cents) stamps and a roll of a hundred 17 cent stamps for $61.00.  On Tuesday, August 9, I used two of the last few stamps on that roll of a hundred 17 cent stamps to mail two number 10 envelopes that weighed - according to my fifteen or twenty year old postal scale - between one and two ounces each.  They were mailed from Bedford, Pennsylvania, that afternoon respectively to Levittown and McConnellsburg, Pennsylvania.
The following Saturday morning, August 13, the one addressed to McConnellsburg showed up in my post office box bearing a scrawled notation: "postage due 3¢".  I gave the clerk a dollar bill and a piece of my mind while she added three cents worth of postage to the envelope and returned my ninety-seven cents change. Apparently the envelope had been to McConnellsburg and back in the intervening four days.  Some fanatical bean-counter in the system somewhere a couple days away had decided to teach a postal regulation scoff-law (yours truly) a lesson and sent the thing back through channels.  The other one - same exact weight, same exact amount of postage - has never returned.
The clerk told me she thought the seventeen cent charge for the second and each succeeding ounce on first class mail had been changed to twenty cents around "tax day" (as she put it) - I suppose April 15 or whatever day this year tax returns were due.
I recall seeing nothing about that increase in postal rates.  Of course, that doesn't mean that there was no public notice given or that there was not some piece in the newspaper about that time.  But I genuinely don't remember seeing anything.  Nor has there been any notice posted in the post office, which I visit daily, since I have a post office box, about the three cent increase on the second ounce for first class mail.
Apparently I have been mailing things that weighed more than one ounce with at least three cents postage due on them since the middle of April.  It took me a total of about five months to use up the hundred seventeen cent stamps.  I am now the proud owner of a roll of twenty cent stamps (purchased August 11), which I have been using conscientiously.
My initial reaction was to feel ill-used by the Postal Service; however, now I am wondering whether a humble penitence would not be more appropriate.  After all, about four-fifths of my mailings of more than one ounce the last five months have been three cents short.  That would work out to a free ride of about two dollars and forty cents I have enjoyed at the expense of the Postal Service.  Maybe I should send them a check, or better yet, buy two hundred forty one cent stamps (or a hundred twenty two cent stamps or eighty three cent stamps) and just put them indiscriminately, if entirely unnecessarily, on envelopes until I've used them all up.
Still, I could wish the Postal Service had been as scrupulous about giving public notice of this rate change as it has been about warning potential armed robbers about the consequences of their intended crime, as in this poster prominently displayed on the door of my local post office:

There must be scores if not hundreds of drug or alcohol-addled, marginally literate, firearm wielding felons dumb enough to want to steal a bunch of junk mail, social security checks or rolls of twenty cent stamps who have been definitively deterred by this very scary, very red notice.  It certainly got my notice.