For example, they recently increased the price of some of the epic PVP weapons to 4.6k conquest points. However, if you try to buy one of these, it doesn't take away 4.6k, but it takes away the cost of what it was in patch 4.0.3.
Tested and it worked on two different toons with two different weapons. It may work on any of the items that had their prices increased in 4.0.6, but this is untested.