[Bluecortina]

It'll almost certainly be a telecine or VT fault, which though I don't know as I'm not sure when they stopped playing film direct to air. 

Difficult to tell what the fault looked like and what is interference caused by the recording/playback of the domestic recording. Although the switch from black and white to colour on the slide could be as it happened on air. AIUI they used to turn the colour bit of the PAL signal off during black and white films. Again I don't know when that ended

Just for info. At the ITV companies I worked for in the analogue days we always switched off the colour burst when txing black and white programmes. We generally did this on the PAL coder on the output of the telecine machine, VTR's would generally switch it off automatically on their output if they detected they were replaying a B&W programme.

Presentation desks generally operated in a 'follow sync' mode - that means the syncs and colour burst on the output of the desk would follow the source that was switched to air, so no 'burst' on the input switched to air meant no burst on the output of the Pres desk. Again where I worked the output of the Pres desk then passed though another amplifier to clean up the syncs and burst. This could either be a Stabiliser (stab) amp which inserted new syncs and burst or a Proc (processor) Amp that added new syncs and burst, new blanking, adjustable black and gain levels with clippers - much more sophisticated than simple stab amp. 

When you think about it Pres desks HAD to work in this mode to enable them to switch between non-sync sources and ensure the sync/burst etc  on the output of the desk was the same (although regenerated) of the input source. An example would be a non-sync cut between a local source (such as a clock) and a non-sync incoming source (such as ITN) - you would likely get a frame roll or twitch at the cut point but nothing else.

Channel 4 always transmitted a colour burst on their output even when transmitting a black and white programme - why? I know not. Even during the period when C4 was passing through the local ITV company for the insertion of ads you were forbidden to alter the C4 signal in any way so the burst remained on.

As for the BBC, I don't know, but I would guess the burst would be switched on or off under the control of the engineer in the network control rooms and so I think what we are seeing here is a simple delayed human reaction to the circumstances of the breakdown.