Have to add:

In Poser 13, antialiasing does the "squishing", too, just like KidRolePlay mentioned.

Only the "unmolested" OpenGL (and the exported final render) aren't distorted.

*

Speaking of exporting: Preview Renders can't be exported anymore using the normal "Tear off" dialog in P13.

This will result in a completely black picture.

Only if you export from the "Recent Renders" bar, will the preview picture be properly exported.