discontinuous QTimeLine problem

Hello,
I am showing and hiding a screen (QWidget type) by using setGeometry function of the widget and a QTimeline object; but there is a problem with timeline..In first show operation after hide operation , the timeline's value is "discontinuous". After latter show-hide operations, it works without problem. I connected my slot like that:
connect(timeLine, SIGNAL(valueChanged(qreal)), this, SLOT(animateWidget(qreal)))
Below is the qDebug output of timeLine->currentValue() . What may be the problem...?

1.000000
0.995858
0.983899
0.964308
0.937394
0.903583
0.863407
0.817500
0.766586
0.705757
0.653014
0.592147
0.523553
0.467037
0.398606
0.343998
0.285690
0.230762
0.175276
0.130184
0.094570
0.061092
0.034536
0.015320
0.003748
0.000000 ==>show operation starts here
0.004555
0.015708 ==>broken values, jumps suddenly to 0.460770
0.460770
0.523553
0.585965
0.647020
0.705757
0.761249
0.812621
0.859063
0.903583
0.934316
0.961940
0.982279
0.995012
0.999938
1.000000