@Pol Another user has already reported the same bug, see:
Thank you very much, indeed it seems pretty much related, so maybe theres not much to do but wait and see if next kernel or firmware from the raspberry 4 devs fixes this. I' ve been reading quite a lot and seems to be that Rpi 4 handles video output very differently from older models, both HDMI and composite outs.
Its also a major letdown for me that its composite out is not only more difficult to set than that of the older Pis but also forces the clocks to a lesser speed (not much they say but its no good news for me). One of the main reasons i got a pi is to connect it to crt... But well, thats another story.
Thanks again for the info and perhaps some one else can confirm certain modes dont work regardless of tv and hdmi cable? Or, on the contrary, maybe someone CAN achive this on Rpi4? Best regards