Kubuntu 17.10 with NVIDIA GTX 1060 6GB
Focusrite 18i8 through qjackctl
i4770k, 16GB RAM
- start Blender 2.79b with fresh config directory
- in user prefs, change audio device to JACK, save user prefs
- open attached demo .blend file
- click button to do OpenGL render: observe that green cursor moves in sync with render, and render speed is normal
- if render is not finished, cancel it
- remove PNGs from /tmp
- click somewhere in graph editor away from frame 1, then shift-ctrl-down-arrow to return cursor to frame 1
- click OpenGL render button again and observe bug:
The second time the render is started, it slows down progressively until it is crawling, and the green cursor does not track the render as it happens (the images are rendered fine). Once this slow-down has happened, I can not render normally, regardless of what I try. If I open the .blend and render without moving the cursor, it renders normally.
Except: disabling "AV Sync" in the timeline, or changing from the JACK driver, causes it to render normally. This seems to happen with Cycles or Blender render, IIRC.
I tried to make a simpler .blend demo with the default cube but could not, so that implies that there is either an additional relevant setting in the project, or that a base level of complexity is required to exhibit the bug.