High CPU usage on a still scene

I am experiencing a very high CPU usage even when there are no changes on a scene.

My usage case is a deferred pipeline, so I modified the deferred-renderer-qml example and disabled all the animations. So it's basically a still frame.

See attached screenshot.

In this case I am (on purpose) on a quad core i5-4590 CPU @ 3.30GHz, with an Intel Haswell card on Mesa:

Vendor: Intel Open Source Technology Center (0x8086) 
Device: Mesa DRI Intel(R) Haswell Desktop  (0x412) 
Version: 17.2.4 
Accelerated: yes 
Video memory: 1536MB 
Unified memory: yes 
Preferred profile: core (0x1) 
Max core profile version: 4.5 
Max compat profile version: 3.0 
Max GLES1 profile version: 1.1 
Max GLES[23] profile version: 3.1

However, I've seen this too on a octa core i7-7700 and an nVidia GTX 960M.

I believe Qt3D is not correctly processing changes on the G-buffer. In this case there are no changes at all, so I'd expect a nearly 0 CPU usage, since all the render textures won't change in time.

Not sure if this behaviour can be seen on a forward pipeline as well, but I believe it's a major blocker when dealing with complex pipelines on Qt3D.

Just for my understanding: is Qt3D core event driven (e.g camera changes, QQ animations, etc) or is it polling every entity on the frame graph looking for changes on every frame ?