Looks like swapRegion (EGL_NOK_swap_region2) is called inappropriately (expected swapBuffers)

When I run for instance "examples/widgets/icons/icons -graphicssystem opengl" on an EGL implementation that does not support "EGL_NOK_swap_region2" then the IP still ends up in eglSwapBuffersRegion2NOK. The application GUI turns up on the screen but any attempt to access the menubar prints out the following confusing error message about success (and nothing of the menu is rendered):

QEgl::eglSwapBuffersRegion2NOK() called but EGL_NOK_swap_region2 extension not present
QEglContext::swapBuffersRegion2NOK(): "Success (0x3000)"

There is this code (in qwindowsurface_gl:500):

if (d_ptr->paintedRegion.boundingRect() != geometry()) {
// Emits warning if not supported. Should never happen unless
// setPartialUpdateSupport(true) has been called.
context()>d_func()>swapRegion(&d_ptr->paintedRegion);
} else
context()->swapBuffers();

But setPartialUpdateSupport(true) is never called from what I can tell and yet we end up called "swapRegion" when we really want to call "swapBuffer". When the application never swaps it explains why the menu and other such items are not rendered. This behaviour seems to break a lot functionality completely (bug has been present for some weeks).