I just noticed that I could not chown files on this newly created HFS+ disk. Using diskutil, I could only see a few noteworthy differences:

$ diskutil info /
[...]
   File System:       Journaled HFS+
                      Journal size 8192 k at offset 0xe2000
   Owners:            Enabled
   Partition Type:    Apple_HFS
   Protocol:          ATA

$ diskutil info /Volumes/disk4
[...]
   File System:       Journaled HFS+
                      Journal size 81920 k at offset 0x1d1e000
   Owners:            Disabled
   Partition Type:    Apple_HFS
   Protocol:          Disk Image

As someone else suggested, I was able to use vsdbutil to enable ownerships/permissions again:

$ mount | grep /Volumes/disk4
/dev/disk4 on /Volumes/disk4 (hfs, local, nodev, nosuid, journaled, noowners)

$ vsdbutil -a /Volumes/disk4
$ vsdbutil -c /Volumes/disk4
Permissions on '/Volumes/disk4' are enabled.

$ mount | grep /Volumes/disk4
/dev/disk4 on /Volumes/disk4 (hfs, local, nodev, nosuid, journaled)