Software RAID 0 looks confusing on dissimilar disks

[M4rtinK]

I've created RAID 0 on two disks - 1 TB & 250 GB. The resulting mdraid volume is about 476 GB big. After this is done, the UI implies that the 2456 GB disk can now hold a 256 GB partition:

This is rather confusing and I have not been able to find a way how to see the real device size once this happens. This could be really confusing if you are trying to identify a disk by size for example.