SSIS works fine in VS until I make change

Hi

I have package that is running fine in Visual Studio package, but if I just open oledbsource in dataflow and click OK without any modifications package immediately fails validation saying can not convert between Unicode and non-Unicode  string data types. So I might have issues with character conversions, but I don understand why package runs smoothly before I force VS to extract metadata again from the database. Is the context in debugging somehow different than the context in the editor.

BR Juha