QTPropertyAnimation not finishing properly

Question

I want to have a button with a click event that opens a frame with an animation. After I upgraded to QT 5 Beta 2, the frame just stopped at the end, leaving a thin line.

I have a QProperty animation and each time I click the button I do this:

if(this->isOpen) {
    this->animation->setStartValue(this->openRect);
    this->animation->setEndValue(this->closedRect);
} else {
    this->animation->setStartValue(this->closedRect);
    this->animation->setEndValue(this->openRect);
}
this->isOpen = !this->isOpen;

this->animation->start();

openRect (300x300) and closedRect (0x100) are set in the init and are never changed.

Does anybody know what's happening??

EDIT

when I click outside the window, the little line disappears