This happens when transferring files both wirelessly and wired ethernet over the network. WD is connected via a TP-LINK TL-SG1005D V6 5-Port Gigabit Ethernet 10/100/1000 Mbps Unmanaged Desktop Switch, via cat 6 ethernet cables to the router.
I also have the EX2 WD network drive plugged into the network switch.
I’ve been transferring from both a Late 2009 iMac and mid 2014 Macbook pro both on OSX El Capitan 10.11.3.
The folders only seem to change names when they contain pictures or MP3’s, however not all folders do this.