I have a c# Fund class with a property of type Dictionary<Tuple<int,DateTime>, int> called Quartiles. I added a number of Fund objects to a collection in mongodb called "funds". They were added without any errors. I then attempted to read back the fund documents from the collection. I got an error trying to access the first document in the collection. The error message said there was a problem serializing the Quartiles property and that an item with the same key had already been added. I then attempted to inspect a sample Fund document using the mongo shell and it looks like it wasn't created properly.

All relevant information is attached.