Can't modify the UDFs I create

I am logged in using an account that is dbo on this database. I created a new UDF, which works fine (I can execute it). When I right click on it in the object explorer and select modify, it says:

Property AnsiNullStatus not available for UserDefinedFunction '[dbo].[fn_MVParamV]'. This property may not exists for this object or may not be retrievable due to insufficient access rights. (Microsoft.SqlServer.Smo)

I would think that if I had the rights to create, as well as use, the function then I should have rights to modify it. I get a similar error if I "script to new window as ALTER..."