Testing R19 and Version 3.07-R1 tonight...
Not sure if this was ever fixed, but I can still not write frames to disc using R19 (R18 does write frames to disc).
There is something to note, when I initialize 'Octane Renderer' from the render settings drop down list, C4D pauses for about 10 seconds (allows no interaction with the UI) and then releases and allows me to work (this does not happen in R18 when I choose Octane in the render settings). Not sure if this helps, but thought I would mention it.