Solved it!!!!
Setting up the depth buffer via Interface Builder seems to not be working. I had to programmatically set it up, and the problem was solved.
NSOpenGLPixelFormatAttribute attribute[] = {NSOpenGLPFAOpenGLProfile, NSOpenGLProfileVersion3_2Core, NSOpenGLPFADepthSize, (NSOpenGLPixelFormatAttribute)24, 0};