EGL context creation ignores the single/double buffering value. EGL allow the creation of single buffered EGLsurfaces, see section 3.5.1 of the EGL specification (http://www.khronos.org/registry/egl/specs/eglspec.1.4.20100721.pdf). The guilty file in qt is src/gui/egl/qegl.cpp

The effects of this are that internals of Qt do allow partial updates on GL surfaces if the surface is single buffered and auto-fill background is disabled, see src/gui/painting/qbackingstore.cpp for details.

As such, under GLES2 environment requesting a single buffered context, Qt internals think the context is single buffered, but in reality it is not and render results are BAD.