As it seems I am unable to post on the Unity Extention forum and there is a problem with the enitre forum workings I will try posing here!!
Regarding this problem Qualcomm you may like to know that this issue is cause when displaying a Unity Canvas with images and buttons.
I removed disabled them in my app and the strange display no longer appears.
So this is either a Vuforia issue or a Unity issue, but as this happens on Unity version from 5.1.2f1 all the way to 5.1.3p3 I think it may be Vuforia?
PS would be nice if someone from Vuforia would give an update on when the forums will be fixed?