Nah, the only space it needs is for the file table and that space is already reserved from the second the drive is formatted.
I think there is a small chance it could be hardware related but I strongly believe that this is a software issue. The reason it doesn't show up on all receivers is the same reason two identical computers with identical parts and software can produce different bugs of their own. For one thing, not all computers/722k's are used alike. Sure, they may be from the same hardware batch, have identical firmware, etc. but do they all have the exact same amount of recordings? Same timers? Same free space? Same settings? There are more variables than just software version and hardware revisions/batches alone.