How to deactivate close button in lubuntu?

[inger]

Hi,
I create my program in qt (c++) with ubuntu OS. I have to move my application to a lubuntu os on another pc. I know how to make a make-file and move the program.
My problem is: I want to disable the close-button in a QTabWidget.

I did it with:

QTabWidget tabWidget = new QTabWidget;
tabWidget->setWindowFlags(Qt::CustomizeWindowHint | Qt::WindowTitleHint);

QTabWidget tabWidget = new QTabWidget;
tabWidget->setWindowFlags(Qt::CustomizeWindowHint | Qt::WindowTitleHint);

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When I use this in Ubuntu, everything works like I want (not able to push close-button). But when I move the programs make-file to lubuntu-PC, the close-button appears again. When I push x (close-button) in lubuntu the program stops.

I need to deactivate this button.
Does anybody know how to do that?