Xcode 10 - NSVisualEffectView added to NSWindow when displayed modally (Mac OS)

I have a NSWindow that I display modally on some other window to display alerts. The code is:

// This code is in MyAlert .m file. MyAlert inherits from NSWindow
- (void)showInWindow:(NSWindow *) {
    [window beginSheet:self completionHandler:NULL];
}

Thing is that when compiled with Xcode 10.1 in a Mac running Mojave I see a gray "blurring" view behind the alert which I don't want there: I want the background window where it's shown to be visible.

Same code compiled with Xcode 9.4.1 does not show this blurring view.

Furthermore, I debugged the UI and there's indeed a NSVisualEffectView inserted in the Xcode 10.1 compiled version which is not there when compiling on 9.4.1, but I can't seem to find a way to get rid of it. Below are screenshots of the UI debugged in both versions.

Has someone faced and figured this one out?

Update (Minimal Project reproducing issue of inserted nsvisualeffectview): http://s000.tinyupload.com/?file_id=43114618701497778758

@implementation AppDelegate

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification 
{
  // Insert code here to initialize your application
  __weak typeof(self)weakSelf = self;
  NSView *contentView = self.window.contentView;
  contentView.wantsLayer = YES;
  [self.window setOpaque:NO];
  [self.window setHasShadow:NO];
  contentView.layer.backgroundColor = [NSColor redColor].CGColor;
  dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3.0f * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
    __strong typeof(weakSelf) strongSelf = weakSelf;
    [strongSelf showAlert];
  });
}

- (void)showAlert {
  DummyAlertWindowController *alertController = [[DummyAlertWindowController alloc] initWithWindowNibName:@"DummyAlertWindowController"];
  [self.window beginSheet:alertController.window completionHandler:^(NSModalResponse returnCode) {
;
}];
}

@implementation DummyAlertWindowController

- (void)windowDidLoad {
    [super windowDidLoad];
  self.properContentView.wantsLayer = YES;
  self.properContentView.layer.backgroundColor = [NSColor blueColor].CGColor;
  [self.window setOpaque:NO];
  [self.window setHasShadow:NO];
  self.window.contentView.wantsLayer = YES;
  self.window.contentView.layer.backgroundColor = [NSColor clearColor].CGColor;
}

@end

You can recover your non-frosted appearance by making your window borderless.

Add this class to your project.

@interface BorderlessWindow : NSWindow

@end

@implementation BorderlessWindow

- (instancetype)initWithContentRect:(NSRect)contentRect styleMask:(NSWindowStyleMask)style backing:(NSBackingStoreType)backingStoreType defer:(BOOL)flag {

    self = [super initWithContentRect:contentRect
                            styleMask:NSWindowStyleMaskBorderless
                              backing:backingStoreType
                                defer:flag];

    return self;
}

@end

And set the window class in your XIB to BorderlessWindow

Lastly set the backgroundColor on the window to get the transparency.

@implementation DummyAlertWindowController

- (void)windowDidLoad {
    [super windowDidLoad];
    //stuff
    [self.window setOpaque:NO];
    [self.window setHasShadow:NO];
    [self.window setBackgroundColor:[NSColor clearColor]];
}

@end

As a side note using wantsLayer to get backgroundColors is better served now by using a custom style NSBox with a custom color or using the backgroundColor property on the window.