Did this ever get resolved?  I am having the same issue with Parallels Version 12.2.1 (41615).  Host: MacOS Version 10.12.6.  Guest: Debian Stretch
On the host:
$ diskutil list
/dev/disk0 (internal):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                         500.3 GB   disk0
   1:                        EFI EFI                     314.6 MB   disk0s1
   2:          Apple_CoreStorage Macintosh HD            499.3 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk1 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Macintosh HD           +499.0 GB   disk1
                                 Logical Volume on disk0s2
                                 C32D2445-D503-48B2-B0D3-8B899D6F1A4C
                                 Unlocked Encrypted
$ ls -ld /Users/bangelo/
drwxr-xr-x+ 67 bangelo  staff  2278 Sep 29 08:09 /Users/bangelo/
On the guest:
$ id
uid=1000(bangelo) gid=1000(bangelo) groups=1000(bangelo),20(dialout),24(cdrom),25(floppy),27(sudo),29(audio),30(dip),44(video),46(plugdev),108(netdev),111(bluetooth),118(scanner)
$ mount | grep psf
Home on /media/psf/Home type prl_fs (rw,nosuid,nodev,noatime,sync)
$ ls -ld /media/psf/
drwxr-xr-x 3 bangelo bangelo 4096 Sep 29 08:10 /media/psf/
 
$ ls -ld /media/psf/Home/
drwxr-xr-x 1 bangelo nogroup 2278 Sep 29 08:09 /media/psf/Home/
$ ls -ld /media/psf/Home/Downloads/
drwx------ 1 bangelo nogroup 170 Sep 28 21:18 /media/psf/Home/Downloads/
 
$ touch /media/psf/Home/Downloads/test
touch: cannot touch '/media/psf/Home/Downloads/test': Permission denied