About Qt Quick2 qml UI flashing and distortion problem?

[hsae]

Hi,
I'm using QtQuick 2.0 to build my UI, sometimes the the UI graphics distorted, the picture, for example, rectangle may change into polygon or line or triangle.... and the UI flashed quickly. after a while, it become back to normal. It seems qqucik2 using opengl to render the whole UI, there are some problems here. opengl do not render correctly. Could any one help?
PS: I have already set qt double buffering.
os: linux atp
device: i.mx6
please see the picture bleow:
P1
P2