Boot OS X Volume appears on TimeMachine after ML install

Hi everybody,

I just upgraded to Mac OS X Mountain Lion 10.8.2 from Lion 10.7.5 (MBP 15" mid 2010). So far, everything went really well.

Today I ejected my TimeMachine Volume (External WD Elements 1.5 TB, 3,5", FileVault 2 encrypted under Lion 10.7.4), when ML asked me, sorry for the translation from german: "TBias I is one of 2 partitions on this hard drive. Do you want to eject TBias I or both?"

Now the strange thing is, that this was for sure not there in Lion. I checked for all hidden partitions (defaults write com.apple.DiskUtility DUDebugMenuEnabled 1), and there are 4 listed with the details underneath:

1) The disc "TBias" Iitself, the only one visible normally (/Volumes/TBias I, encrypted, 1.5 capacity, capacity for whats occupied and free)

2) disk2s1 (not activated, EFI, 209.7 MB)

3) TBias I (not activated, pysical core storage volume, capacity 1.5 TB) --> is this normal? I have a second WD 1.5 TB where only disk1s1 appears?

4) Boot OS X (Volumes/Boot OS X, capacity 134,2 MB) --> even though it says its Mounted, it doesn't show on desktop or anywhere.

TimeMachine is working just fine, but I would like to get rid of this message that appears everytime I try to eject the volume. Unfortunately, I don't know if I can erase "Boot OS X" safely or not. I also didn't find anything about this newly appearing partition on an external TimeMachine Volume.

So my questions:

- Why did this appear?

- Can I safely erase this partition to get rid of this message?

- is the second TBias I, hidden partition normal? On my other WD 1.5 TB it does not appear

Thanks for your help, I appreciate it.

Best,

Tobias