I have quite a complex typed DataSet, with multiple Elements nested within each other and linked by various foreign key constraints. It appears that such a complex data structure results in a constraint violation exception thrown when top level Element's primary key is updated and that change begins propagating down to all of the nested children.
I have recreated the problem in a tiny project, which can be downloaded here:http://fedot.stockworm.com/misc/XSD.zip
Please note, that an Exception is thrown when the following line of code is executed:

dataSet.Brand[0].BrandName = "Nissan";

Also note, that removing foreign key constraint between Color and ModelColor elements eliminates the Exception and performs all foreign key updates properly. However, I am trying to understand why I cannot keep that key and still have everything working right.
Please download the project, execute it, and see everything for yourself. Thank you in advance for hopefully shedding some light on this problem.