If you look at the DataGridViewTextBoxCell property, ValueType, in reflector, you can see it overrides a property from DataGridViewCell.
The strange thing is, is that the overriden property is readonly, but the property in the parent class is read and write.
I can only presume that the property has been shadowed and reflector doesn't ...erm .. reflect this.
Is this right?
eta: I'm looking at the source, in reflector, as vb.net.