Sometimes a small area of the graphicsvideoitem does not have video rendered to it on Symbian

Sometimes a small area of the graphics video item does not have video rendered to it, and appears transparent so you can see through to the application below.
This has just been seen in the top right hand corner of the video item, and only occurs when there are multiple video items (or 1 video item and 1 camera).
It has only been seen with QCIF H.263 and QCIF MP4 (these formats support multiple video items).
It is quite hard to reproduce, but the following steps seem to work:
1) Start declarativevideo test app, set 2 H.263 test files
2) Launch video-multi.qml : both videos appear ok
3) Rotate phone to horizontal, then back to vertical : both videos appear ok
4) Tap screen to return to menu, then relaunch video-multi.qml or video-camera.qml : top video appears to have a transparent "square" in top right hand corner