Unresolved "using" does not produce an error

[ssrmm]

The following Code does not produce any errors and is even working at runtime:

namespace Test
{
  syntax module Test
  {
    using Nitra.Core;
    using Inexistent.Namesace;

    [StartRule]
    syntax Expression
    {
      | Foo = "FOO"
      | Bar = "BAR"
    }
  }
}

Since using Inexistent.Namesace; references something that doesn't exist, I would expect a compiler error instead.