This is my work flow:
1.make a low poly in Max 7.1
2.Export to ZBrush(iFlipY,eFlipY,iSwitchYZ,eSwitchYZ)
3.divide,sculpt,normal map, flipY,export the map
4.in Max,normal bump it.Because the map has flipY in ZBrush yet,no need any Tiling ‘-1’.
5. 
,if use normal bump,half good,haif fliped.
if anyone can solve this? Thanks!
you should not use normal map on a mesh with flipped normals.
the only thing for you to do is to go back to max and re UV your mesh and do the entire model in one shot.
then reimport that low rez as your tool, u should have no probs re baking a new norm map with the newly uv’ed model.
After mirror,before attach,all seem good.
once u attache it becomes a new mesh, so the vertex order is changed.
Thanks,I must work more.