Version Used:
VS 15.9.11.

Steps to Reproduce:

public class Foo
{
    public IEnumerable<object> Bar()
    {
        yield return ("test", (decimal?)1.23);
    }
}

Expected Behavior:
No suggestions.

Actual Behavior:
Roslyn suggests a fix:

This fix breaks the program's semantics, since the actual returned value's type changes from ValueTuple<string, Nullable<decimal>> to ValueTuple<string, double>.