I never do the export/import process for that exact reason.
If I need to move a VM for some reason, I copy the entire VM directory to the new location then open VirtualBox and use "Machine" -> "Add ..." and select the directory with the VM config and files.
I've not moved VM's between Windows and Linux, but it works fine going back and forth between OS X and Windows. The only caveat being that you have to re-visit the VM's settings for things like host volume mapping and especially networking config.
If I need to move a VM for some reason, I copy the entire VM directory to the new location then open VirtualBox and use "Machine" -> "Add ..." and select the directory with the VM config and files.
I hope that helps, unless I missed something.