QWT + release mode compilation error

Hello,

I am developping an application using QWT.
I used QT4.7.4 + QTCreator + mingw4.4 + QWT 6.0.1

I create a class derived from QwtPlot to draw a CPU graph
I had no problem to compile on debug mode. But on release mode, I have the following errors :
- undefined reference to `QwtPlotCurve::setSamples(QVector<double> const&, QVector<double> const&)'
- undefined reference to `QwtPlot::QwtPlot(QWidget*)'
- undefined reference to `QwtPlot::setAutoReplot(bool)'
- ..................


Have you already enconter this type of error


Best regards,

VPM

Did you compile qwt in release mode?
Do you link against release version of qwt?