This is a question sometimes heard by carpet cleaning companies from customers after cleaning their carpets. They have to explain that buckling occurs either because the polypropylene backing on the carpeting is defective or, more commonly, the original installation was not done properly.
Sometimes installers don’t take the time to stretch wall-to-wall carpeting (they are often paid per house, not by the hour). The slack can be up to 1%, or an inch for every 100 inches of carpeting. Without stretching, buckling or bunching usually shows up around the edges and heavy furniture. It may appear after a few months or after a visit from your carpet cleaner. If you’re having carpeting installed soon, make sure the installers don’t just “knee kick” the floor covering into place. Not only ask for power stretching, insist on it. For more on quality installation see http://www.carpet-rug.org/residential-customers/installation/index.cfm