ZBrushCentral

Displasement map break on some edges

Hi to all. My friend was modeling a seahorse and than import it for detailing in zbrush. Whan he finish with detailing, he export displacement map, and there he get problem. On some parts, on UV seams, his displacement brake. Here is pictures of it.

http://img810.imageshack.us/i/zbrushproblem.jpg/
http://img850.imageshack.us/i/zbrushproblem2.jpg/
http://img641.imageshack.us/i/zbrushproblem3.jpg/

Does anyone know what causes this problem?