OK,  I've come across this and I think I know the solution.  I believe it is a rounding error within Poser as it tries to round off the co-ordinates of any ".obj" file that uses more than 6 digits per axis.  Your example has 10 digits to represent each co-ordinate and that will cause Poser to create errors as it rounds them down to 6 digits.

For a solution (or test) download a modelling program called Silo2, load your model into it, then save out as an obj file.  Silo2 will correctly round down the co-odinate numbers and hopefully the lighing issue will be solved within Poser.

Silo2 is free to use for 30 days, then after which can be used as a file converter.

check it out  http://www.nevercenter.com/

( I found this out while using Wing3d which operates at an 8 digit resolution)

good luck
jdc