Sounds like poor joint quality. Are you using a butt joint or a notched wedge joint? The latter reportedly acheives better compaction in the joint area.
To deal with the existing problem, a proactive pavement management program is probably your best bet, sealing cracks as they occur, before water can enter and create potholes.
Considering the timing of your post, can I assume that this is a freeze-thaw problem?
"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928
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