BBC One Problems

That jump is the extra delay associated with putting a DVE into the signal path to perform the squeeze. Amazing that the BBC allow Red Bee to get away with such a bodge on their (supposedly) top-drawer services !

Yep - and it isn't there on the HD version thank goodness. (Though I hate the things and wish they'd go away entirely)

I think they push back is done live - hence the DVE frame jump - however I suspect they were rehearsing without the mixer in rehearsal mode, or without The One Show switched directly to line downstream, and thus as they triggered the push back (which had the EastEnders video coming off the server that they were previewing it on) the DVE/keyer was cut to line, and they cut away from The One Show?

Just to confirm, the error is included in the iplayer version...
http://bbc.co.uk/i/s9wkv/?t=18m15s

Does this explain that little jump that credits always have just before the ECP appears?

My understanding of the playout software is that they can effectively bypass what's going out and preview the next junction or other sequence in the future. The interface is like an edit time-line so the director can adjust timings and tweak transitions as they wish. Before they could check individual items but had to do a junction or a credit squeeze once - live on air!

Yes, the jump is the moment the DVE is switched into circuit and the associated delay is introduced. Because it's often during scrolling end credits, the jump looks terrible as your eyes naturally read the credits and therefore the jump looks very visible (it wouldn't be as bad if it was done during action but I doubt BBC One would tollerate them doing it).

Indeed, the director can copy and paste a sequence from the channel's schedule into a 'preview' channel. The software puts the on-air channel into bypass and uses the vision mixer to show the director exactly what will happen in the next junction including IPPs, Squeezes, GFX elements, trails, ident and any recorded announcement. If needs be, the live announcer can join in on rehearsal too.

Ironically, this functionality was built in to the old manual control rooms which closed in 1996. Junctions were routinely reahearsed and fine tuned. The automated control rooms that were used from 1996 to 2000ish were supposed to have a rehearse mode, but they never ever got it to work properly. The idea wasn't ever put into the Digital Control area used from 1998 - 2003/4, and only returned to the architecture at the broadcast centre.

The jump everyone's referring to used (may still) happen on BBC 1 Scotland's analogue service. It's been over 10 years since I've watched analogue TV, so it was long before credit squeezing existed; what would be the reason for that?

Maybe you're referring to the point where the Scotland continuity was switched in and out of circuit. The same thing happened in wales AIUI and it was even worse in NI I believe.

This is all correct, the error on the One Show was that the Graphic device was stuck 'on' on the main channel from the Next slide going into the One Show. The Main and Preview channels share the graphics device used to generate the squeeze so hence when the director tried to rehearse we saw it on the main channel.

In Northern Ireland (and Scotland and Wales too I'm fairly sure) you don't run the danger of this fault...

...as when they click on 'Preview', the highlighted part of the schedule is automatically copy&pasted in a preview stream which has its own graphics hardware which is not shared with the main playout stream.