QToolButton setStyleSheet works on win8, not win7?

Question

The following works perfect on Windows 8.1, but not on Windows 7. The problem is that on Win7 setStyleSheet has no effect (compiled on 8.1 and deployed to 7).

Any explanations or workarounds?

QToolButton* button = findChild<QToolButton*>( QString::number(buttonIdx) );

button->setStyleSheet("background-color: yellow; border-style: outset; border-width: 3px; border-radius: 5px; border-color: red; font: bold 10px; min-width: 1em; padding: 3px; ");

Answer 1

Problem was that I upgraded earlier from Qt5.2 to 5.4. I didn't include the newer qt-dll's and platform in the deployment.