well.. IMO there's nothing that can be fixed.. if you install SME on a single disk (raid1 degraded) and then add a disk which is smaller... 
The bug is that the second disk isn't smaller than the first!
I made following experience on the VM:
- 2 disks defined with 20GB
- installation on disk#1 and add disk#2 later --> disk#2 too small
- erase both disks (NOT create others!)
- installation on disk#2 and add disk#1 later --> disk#1 too small.....
--> the last added disk is seen smaller than the first one in any cases.
IMHO it isn't normal.
Bye
Arnaud