Odd result in NetBIOS file share list

I'm puzzled how this can be happening.

Local network all of windows 8.1 pcs, all with NetBIOS settings enabled, same NetBIOS network group name, home groups disabled (sharing using name/pw) and shares working. Call them PC1 to PC4.

Each of them can file share or remote desktop to any of the others by name, or ping. So the networking's actually working.

What's odd is that for each of them, windows explorer only lists PC1,PC2,PC4 under "network". Even on PC3 it can't "see" itself according to windows explorer. But net view in a command prompt shows all of them have PC3 listed.

Also if I manually type \PC3 into windows explorer it works, PC3 is added to the networks in the navigation bar - but still doesn't appear in the pane on the right when I'm on "networks" even at the same time its showing in the right pane. It can explore its files just fine. But it won't show up by default in the nav pane (although all others do) and when it does show up in the nav pane after manual entering it won't appear in the right as a network location although it will show the folders if selected in the nav bar.

How is this inconsistent behaviour happening and what might be configured on PC3 causing this? Or is this a windows explorer specific issue and explorer is caching locations and got confused?