Tire Bead problems of the 1998 Dodge Caravan

Four cooper futura 2000 lte p205/70r14 tires (dot u9ke xad3906) were replaced onto my minivan wheels on 4/4/2011 after sitting for 16 months in protective bags in my garage. They are touring tires and were swapped out for the cold weather tires that had been on the van for the previous 16 months. On 4/5/2001 the two rear tires lost their bead within 50 miles of being reinstalled. This is perhaps only the third time being put on their wheels. Upon inspection by a qualified tire installer it was determined that both beads had failed. The first failure occurred after driving 25 highway miles. At which time the tires was replaced with a new tire. The second failure occurred after the 25 mile return trip during a turn from the expressway exit. Both tires were determined to have failed for the same reason by the aforementioned installer. The tires were purchaced on 5/24/2007 at pepboys auto store 0289 5630 s. Westnedge Ave. , portange , mi 49002.