Can't create/mount snapshot

Hello all,                                                                                                                                                           
                                                                                                                                                        
I am on a recent (last few days) build of current. I am unable to create and mount a snapshot, as the following sequence shows:
                                                                                                  
root_at_freebsd:~ # mksnap_ffs /.snap/snap                                                                                                                                                                                                                                                 
root_at_freebsd:~ # echo $?                                                                                                                                                                                       
0                                                                                                                                                                    
root_at_freebsd:~ # mdconfig -a -t vnode -o readonly -f /.snap/snap -u 4                                                                                                
root_at_freebsd:~ # mount -r /dev/md4 /mnt/snap                                                                                                                         
Superblock check-hash failed: recorded check-hash 0x890ef5e3 != computed check-hash 0xdb34ad30                                                                       
mount: /dev/md4: Invalid argument                                                                                                                       
                                                                                                                      
My `uname -a` output is as follows:                                                                                   
FreeBSD freebsd 13.0-CURRENT FreeBSD 13.0-CURRENT #0 r340519: Sun Nov 18 05:36:55 UTC 2018     root_at_freebsd:/usr/obj/usr/src/amd64.amd64/sys/GENERIC  amd64                                                                                                                             
                                                                                                                                                                                                               
Does anyone have some idea what could be going on?                                                                                     
                                                                                                     
Thanks,
btv