sys-block/gpart-0.1h-r2 fails to analyze disks larger than 2GiB. This is because the (patched) l64seek() function just calls lseek() which only does 32-bit seeks (on 32-bit architectures) unless compiled with LFS support.
Created attachment 252913 [details, diff]
Ebuild patch for LFS support
Patch to compile gpart with LFS support for disks greater than 2 GiB.