Well, I know roughly 10 GWX files (of the 2000+ or so?) gave problems when I tested them. I talked to ref and privateer about it a while ago. And they fixed them (in your private build). They weren't really critical issues, but yea, S3D won't open those few.
Oh, and if you find bugs, please report them
[edit] The import chunk bug is fixed in v0.7.1
