I have a Lynx BMS not the VE Bus BMS so I have not seen it, when the BMS stops charge like you have shown on BTV cable failure, the BMS tells the Cerbo to set charge current to 0 and DVCC tells the MPPT to stop charging, works as intended. I have no problem in believing that when required, solar will be shut down by the BMS as advertised, mine does, your does as you have proven.
The problem comes when you shut down the BMS, then it is no longer sending comms to the Cerbo, in fact the Cerbo may shut down if not auxiliary powered so there is no message to the Cerbo to stop charging, so the MPPT goes into stand alone operation and does not shut down. This same issue has been discussed recently on the Lynx BMS. On my BMS, of the 3 options, I added a breaker between the panels and the MPPT because if I am going to shut the system down, then I want to make it properly safe rather than relying on the software shutdown of the MPPT with high voltage still present on its input.