QQuickFramebufferObject always eats 100% of one core

QQuickFramebufferObject always eats 100% of a CPU core, even when no OpenGL rendering is performed. Tested on Windows and Linux but only happens on Windows. I'm using Core OpenGL 3.3 (not ANGLE).

To replicate, open the "Scene Graph - Rendering FBOs" example or create a QQuickFramebufferObject and just call "update()" inside the render function.

Pretty sure this is a regression since I've been using QQuickFramebufferObject for a while but never noticed this, not sure if it's from Qt or Windows though.

 EDIT: Always happens to me now, focus doesn't matter.