Chinese bellflower

The seeds that I planted in spring had a lot of buds. Beautiful flowers bloomed one after another, but one of them was unusual.
The petals of them are generally divided into five on the top, but the petals of this flower divided into only four.
Is this the flower of the mutation?
I hear that malformed flowers have increased recently. Is this one of a deformity?

took on October 2008.

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