QTextCharFormat setFont & QTextEdit zoomIn

I have an issue with QTextCharFormat::setFont() and QTextEdit::zoomIn(), the issue is, when I set the font with:

Code:

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QTextCharFormat format;
format.setFont(font);
Notepad::Tab->TextEdit->mergeCurrentCharFormat(format);

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When I zoom, there are no effect. Whereas before with the default font there are no problem.

What am I doing wrong?