Grrrr.... happened on two drives now (different external USB enclosure, one is USB 2 and the other is USB 3).
Both drives have been identically partitioned under OS X as a GUID and split in three parts: OS X (running Mountain Lion on one drive and Lion on the other drive), Time machine and the remainder ExFAT.
Surprise, surprise - after booting in Windows 8 I find both of these as MBR, they've been silently converted from GUID by Windows 8. Not impressed.
Both drives have been identically partitioned under OS X as a GUID and split in three parts: OS X (running Mountain Lion on one drive and Lion on the other drive), Time machine and the remainder ExFAT.
Surprise, surprise - after booting in Windows 8 I find both of these as MBR, they've been silently converted from GUID by Windows 8. Not impressed.