What is the point of a synchronized lock on a single return statement?

[Andrej Mitrovic via Digitalmars-d-learn]

From: 
https://github.com/dlang/phobos/blob/10b9174ddcadac52f6a1ea532deab3310d3a8c03/std/concurrency.d#L1913-L1916:

-----
///
final @property bool isClosed() @safe @nogc pure
{
    synchronized (m_lock)
    {
        return m_closed;
    }
}
-----
I don't understand the purpose of this lock. The lock will be 
released as soon as the function returns, and it returns a copy 
of a boolean anyway. Am I missing something here?