setMovable flag doesn't work

[linuxsable]

@implementation MenuWindowController

- (id)init {
    if (self = [super initWithWindowNibName:@"MenuWindowController"]) {
        [self.window setMovable:NO];
    }

    return self;
}

Expected: window is no longer dragable. Results: window is draggable. Converting window to NSWindow via NIB fixes the issue.

Thanks.