Widget->show() place widget to top left corner (not on the top of mainwindow)

[Zlatomir]

I'm not sure that i understand your code, but:
this:

this->about = new DialogAbout(parent);

this->about = new DialogAbout(parent);

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shouldn't be like this?

this->about = new DialogAbout(this);

this->about = new DialogAbout(this);

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