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Never realised that, you can't just select system module for blocks admin or at least in 2.0.16 (I not tried .17)
It's been a while since I tested 2.2 X, I'm sure it's possible in there though, if so I'm sure that option will be supported in future X versions.
If you want them for your account/profile section, you could always consider a profile module, that would work.