Dain the Caswallen's favorite wonder, for which he grants a better diplomatic relation, is the Pagan Temple 
This seems to be because his section of the Civ4leaderheadinfos.xml has the line:
Whereas Thessa has
Also, Dain has the line
Whereas Thessa has
Though judging by the other leader sections Thessa is the one who has the wrong value for that variable.

This seems to be because his section of the Civ4leaderheadinfos.xml has the line:
Code:
<FavoriteWonder>BUILDINGCLASS_CATACOMB_LIBRALUS</FavoriteWonder>
Whereas Thessa has
Code:
<FavoriteWonder>BUILDING_CATACOMB_LIBRALUS</FavoriteWonder>
Also, Dain has the line
Code:
<iFavoriteEarlyWonder>BUILDINGCLASS_CATACOMB_LIBRALUS</iFavoriteEarlyWonder>
Whereas Thessa has
Code:
<iFavoriteEarlyWonder>BUILDING_CATACOMB_LIBRALUS</iFavoriteEarlyWonder>
Though judging by the other leader sections Thessa is the one who has the wrong value for that variable.