Modo has a symmetry checker/fixer tool which hilights the exact verts which aren't symmetrical.

According to Modo the V4 base mesh is perfectly symmetrical if you open the source obj directly in modo without involving poser. Once V4 has been loaded in poser, zeroed and exported she is way off, only her midriff and face/scalp are still symmetrical.

M4's base obj isn't quite perfect, one iris is off and about 100 other verts sprinkled all over him are very slightly off (a 'fix' threshold of 5 micrometres is all that's needed to fix them). Once he is exported from Poser his entire mesh is completely off so I'm guessing his center must have moved during the loading/exporting process.