Let's just analyse this from counsel's viewpoint. The officer in the case is commonly in court while other evidence is given. Prosecuting, I often had him court That's because what he is says isn't affected by what other witnesses say, we know what he'll say, it won't be affected by what they say, and it is not contentious in real terms. That is not always so, but often is. The defence know he's in and can always ask for him not to be; you ask them whether it is all right for him to be there. Defending, I would be well aware, and would say no otherwise. It is often a help to everyone to have him in court; from the prosecuting counsel's point of view, he understands and knows the case better than some CPS clerk, and the same may apply to defence counsel , who has him on tap as proceedings as going along and have details cleared up without having to get messages sent out.
How was a witness 'unscheduled'. If she was fully bound [subject to a requirement to attend] she'd attend. If she was conditionally bound [not so required] that was because the defence didn't want her there and were happy for her statement to be read out as evidence.. They were not challenging anything in it and had nothing material to ask her. Now it may happen that there is some detail which she could give, and which is not clear from the statement but it is not particularly important. Then we hold any ambiguity or missing detail in the defence's favour; here, if they really wanted the witness, what could be her evidence, not in her statement, was suddenly important to them, they could have had her brought, if not then ,on the next day. If the potential evidence was case turning and had not been foreseen, then she would have been. "Child care issues" would not stop that whether there were any or not. I think we can conclude that the evidence was not, but just something which defence counsel thought he might like to ask about if she was available, but if not, it didn't matter. She hadn't been fully bound by the defence's request, so it can't have seemed that there was anything important that she could say; if it was apparent that there was, they'd have had her bound to attend