I've detected that, in blog_check_and_install_blocks(), called each time one user access to his blogs page the first time, two blocks are created.
Such block creation doesn't include information for dataconfig at all, and such field in DB is defined as mandatory (NOT NULL).
So, one of these is true:
1) The calls ("2") in the functions above are wrong and should include dataconfig.
2) The dataconfig field must be declared optional (nullable).
In logic, I think that 2) is the correct one, but need confirmation.