I have a bug in the pie chart "By virtual Machines" in the Performance section of my 2 datastores. The pie chart is good and the names of the VM in the list are the top 5 VM that take the most space on the datastore. But the name are not in the good order. The problem can be verify with the informations Virtual Machines section in Related Object of the datastore.
I have just upgrade to vCenter Server 6U2 but i don't know if i had the problem before.
Have you the same problem ?
I think, this is known issue and there is high chance it may get fixed in upcoming VC release. You can raise support request with VMware as well.