There seem plenty of entries here for Event ID 58 The disk signature of disk x is equal to the disk signature of disk y, but I haven't yet seen a proper resolution.
I'm using a daily scheduled WSB on a 2012R2 hyper-v host server with a 2008R2 guest and getting (on the guest):
Log Name: System
Source: partmgr
Date: 30/10/2014 02:01:38
Event ID: 58
Task Category: None
Level: Warning
Keywords: Classic
User: N/A
Computer: servername.dom
Description:
The disk signature of disk 5 is equal to the disk signature of disk 4