C# compiler fails to error when it should

The compiler fails to detect that line 3 will error:

IList<IList<double>> xs = new List<IList<double>> { new List<double> { 2 } };
IList<string> x0 = xs.First();      // does not compile, as expected
foreach (IList<string> x in xs) { } // works, unexpectedly!

(Even though there’s no error, Visual Studio does suggest on line 3 that there is an implicit cast, which may fail at runtime.)

Interestingly, the compiler successfully detects the issue here:

IList<double> xs = new List<double> { 2 };
string x0 = xs.First();      // does not compile, as expected
foreach (string x in xs) { } // also does not compile, as expected

Is there a good reason why line 3 just gives a suggestion and not an error, like in lines 2, 5, and 6?

>Solution :

foreach is just :

try {
    while (enumerator.MoveNext()) {
        IList<string> x = (IList<string>)enumerator.Current;
    }
}

The question boils down to – should this be a compile-time error:

IList<string> x = (IList<string>)enumerator.Current;

According to the 10.3.5 Explicit reference conversions section from the language specification regarding allowed explicit conversions:

From any interface_type S to any interface_type T, provided S is not
derived from T.

So, the answer is no.