Bracks was appointed in May 2013 by Gillard. Labor had no obligation to consult with the Coalition regardless of the fact that the election date happened to be known and regardless of the fact that Bracks' appointment would take effect during the caretaker period. The possible outcome of the election held no sway over the appointment; an appointment needed to be made and Gillard was the PM so she made it, that is all.
BUT
The Coalition does have the right to revoke the appointment upon forming Government.
Now Labor knew this but as Jaekus notes Labor were polling well at the time and despite the endless rhetoric which we have all become so familiar with saying Tony Abbott was the destined saviour of all, the election wasn't a foregone conclusion. Labor could have reasoned that given there was a Federal Election and given there was the potential for a change in government they should negotiate with the potential incoming government on appointments. But why would they do this? What message would that send? You could be damn sure the Murdoch Machine would have picked up on it and no doubt the Coalition would have ended up crowing about how the Labor Government knew they were doomed. There was nothing to gain by Labor doing this, plenty to lose, and no requirement to do it.
Bracks also knew his appointment wouldn't be secure if there was a change of Government. What he could have done is contact the Coalition himself to seek their approval. It would have been nice if the Coalition backed him too - after all he is qualified, he was a very successful Premier and spend a lot of his post-political life guiding the Government in East Timor pro-bono. But the Coalition wouldn't have approved him and Bracks would have had to either decline the position and basically open the door for the Coalition to manhandle the Labor Government, or do what he has done and just assume Labor would win or the Coalition would be too preoccupied with things that actually matter to worry about him.
So we're in a position now where the Coalition wants to stamp their authority on things and Bracks is in their sights.
Bracks is most definitely a Labor man and his appointment was in part a recognition of this - standard in these sorts of things on both sides, no reason for this to offend the LNP as much as it apparently has. But the move to revoke his appointment is purely a recognition of his Labor ties. Julie Bishop said at the time of the appointment that she felt she had the right to be consulted, (she did not,) and the Government didn't have the right to make these appointments after the election had been announced, (it did,) but no-one seriously thought she'd actually care about it post-election. Her move to follow through and have it as her first act as Foreign Minister is churlish and mean-spirited - completely in-keeping with her character.
Bishop argued Labor's appointment of Bracks was unethical and inappropriate. Not true at all, it was completely their prerogative to appoint him and Bracks is an appropriate choice for the role.
Tanya Plibersek argued that the Coalition's decision to axe the appointment was petty and vindictive. This is true. Bracks is being axed because he's a Labor man and the Coalition want to grasp the opportunity to appoint one of their own. It's payback politics, nothing more.
There are rumours that they want Nick Minchin, a former Howard Minister and current "faceless man" who claims tobacco companies are unfairly treated and climate change is a leftist conspiracy - but a good loyal Liberal man all the same. I hope it's someone else but I haven't been wowed by the Coalition's ability to make good decisions just yet. Hell, I hope it's someone who's politically neutral but I'm pretty damn sure it'll be a loyal LNP-associated savant of some description.
Edit: Also for interest's sake, when Rudd booted out the former Coalition he not only kept Liberal appointees but also appointed high profile Liberals Tim Fischer and Brendan Nelson to diplomatic roles.