The issue has already been reported on the Arch Linux forums and bug tracker, as well as bug #12128 on the VirtualBox Bugtracker (sorry, can't post links). It seems like it's most related to the kernel itself, seeing how the host OS and VirtualBox version are irrelevant to its occurrence. Keep in mind that this issue also happens with the stable release of VirtualBox, so the mods should consider moving this thread to a different forum.
Seeing how the application seems to hang on getdents() (according to the strace output posted by one of the users on Arch Linux forums), perhaps dirops.c from changeset 47588 is the culprit?
A plastic bag stranded at the lights, this once was me!