In VS2008, the dataset has a separate file (from the .designer.cs) where the user can use a partial class to write custom code. If this file contains more than one parital class for the dataset, the designer changes the namespace on the second partial class to the namespace of the table adapters.
I have 2 partial classes with the same namespace because one is code generated (custom system) and one is hand crafted code. Every time I save changes in the dataset (or run custom code), the designer changes the namespace from ProjectName to ProjectName.DataSetNameTableAdapters.
This caused a lot of problems to first diagnosis and causes continuing irration to remember to change the namespace back after generating.