QDialog goes behind the file save dialog on Mac OS

Dear All,
I have a problem on Mac OS El Capitan.
QDialog goes behind the file save dialog on Mac OS, though I have tried different flags including Qt::FramelessWindowHint |Qt::WindowStaysOnTopHint | Qt::X11BypassWindowManagerHint flags.

I am using Qt 4.7.3.

strange behavior is in works first time only and second time it goes behind in same situation.

Thanks,

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Added after 26 minutes:

Qt::FramelessWindowHint|Qt::WindowStaysOnTopHint|Q t::Sheet
This works fine.

Thanks,