Comment 4 for bug 416499

I believe that's because W7's installer produces incorrect partition table. Here is parted session on such disk:

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ubuntu@ubuntu:~$ sudo parted /dev/sda
GNU Parted 1.8.8.1.159-1e0e
Using /dev/sda
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) p
Warning: /dev/sda contains GPT signatures, indicating that it has a GPT table. However, it does not have a valid fake msdos
partition table, as it should. Perhaps it was corrupted -- possibly by a program that doesn't understand GPT partition tables.
Or perhaps you deleted the GPT table, and are now using an msdos partition table. Is this a GPT partition table?
Yes/No? yes
Model: ATA WDC WD3000GLFS-0 (scsi)
Disk /dev/sda: 300GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number Start End Size File system Name Flags

(parted)
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From what I can guess from the warning above parted tries to get partitions from that fake MBR table. What I can't understand is why not to read GPT table (as soon as parted seems to be able to recognize its presense)?