Yes, this is a known issue. Go find it in the Ideas Lab and VOTE for the fix. I know, it sounds corny to go vote to fix a bug, but supposedly it increases the priority.
WD might not consider it a bug; it may be working “as designed.” Supposedly it does not do this if the storage is directly attached.
I could very well be wrong, but I think this has to do with samba itself rather than the device. Since the drive is seeing it as a simple Samba share, it is displaying what it finds. Samba doesn’t have the ability to filter based on extension or file-type. I think the fix would need to be made on the computer side (i.e. every major OS and NAS drive).