Databinding and Nullable does not seem to work together

Can someone explain why data binding against a nullable property in an ADO Data Entity Model does not seem to work. I have a decimal field named "Weight" that when it is set to allow nulls in the database, I can not seem to change the value on a windows form. However if I turn off the allow nulls in the database and update the model, the databinding works as i expect. Looking at the Designer.cs file the only difference I can tell is the underlying value seems to be a decimal versus a decimal开发者_如何学运维?.

It may be related to this nasty bug (there was a microsoft connect bug report, but the EF team apparently deleted all the bug reports...)