Capturing self instead of using self. in switch case in DispatchQueue causes compiler error

I have an @objC used for notification.

kTag is an Int constant, fieldBeingEdited is an Int variable.

The following code fails at compilation with error: Command CompileSwift failed with a nonzero exit code if I capture self (I edited code, to have minimal case)

    @objc func keyboardDone(_ sender : UIButton) {
        
        DispatchQueue.main.async { [self] () -> Void in
            switch fieldBeingEdited {
                case kTag : break
                default : break
            }
        }
    }

If I explicitly use self, it compiles, even with self captured:

    @objc func keyboardDone(_ sender : UIButton) {
        
        DispatchQueue.main.async { [self] () -> Void in
            switch fieldBeingEdited {  // <<-- no need for self here
                case self.kTag : break  // <<-- self here
                default : break
            }
        }
    }

This compiles as well:

    @objc func keyboardDone(_ sender : UIButton) {
        
        DispatchQueue.main.async { () -> Void in
            switch self.fieldBeingEdited {  // <<-- no need for self here
                case self.kTag : break  // <<-- self here
                default : break
            }
        }
    }

Is it a compiler bug or am I missing something ?