My temporary solution is to use NFS shared folders instead of vboxfs, as vagrant does.
From osx "/etc/exports" (place this to the beginning of the file):
/Users -mapall=[youruser]:[yourgroup] [boot2dockerip]
Restart the nfs daemon in osx:
sudo nfsd stop && sudo nfsd start
From boot2docker umount/remount /Users using NFS:
sudo umount /Users
sudo /usr/local/etc/init.d/nfs-client start
sudo mount 192.168.59.3:/Users /Users -o rw,async,noatime,rsize=32768,wsize=32768,proto=tcp