I fly mostly international and find it happens all the time (as I several take days or weeks of monitoring fares before I commit myself). Often I find the changes are in my benefit (find cheaper fares on repeated checking). Availability of different fare classes can change. Also factors such as the exchange rate and oil prices impact on the fare cost so you often see smaller changes from day to day or hour to hour. Often my experience is when price goes up by say 100 dollars it is best not to grab it but wait and within a few days it often comes back to baseline - sometimes I get the impression the airlines are just testing the market. I flew NWA transatlantic last month and the fare was about 500 dollars when I started checking then suddenly about 3 weeks to christmas the fares went up within an hour to about 3,000 return for the available classes which were now B or Y only; these high fares remained for almost a week then all of a suden one day (about 9 days to departure) the fare came down to $590 (mixed Q and B) - even a B fare return which was 3,300 earlier it the day was now listing at $690.

I rarely buy flights earlier than 2 weeks to my departure and almost always find that fares get cheaper as the flight approaches.
Just to illustrate checking on NWA.com for DTW-CDG return for a 7 day stay departing

Feb 14 $544
Mar 14 $544
Apr 14 $661
May14 $756
Jun 14 $1056
Aug 14 $1058

Whilst I accept seasonal variations exist, it seems odd to me that you pay a premium for the privilege of making your travel arrangements early as I am sure that as the departure day approaches cheaper seats will become available.