PhaseOne have responded to my support case with the recommendation that the workaround for now is simply to revert the profile in the output recipe back to the intended one.
I can confirm that the identical issue is present even when the embedded camera ICC profile is set to 'No Color Correction'. I remain very concerned by the apparent changes in the output file itself, as I use this specific configuration for generating custom camera profiles for art repro. Clearly it's not possible in this case to make any profile changes in the exported file, and any subtle (or not so subtle) incompatibility with the profiling software would be a disaster, especially if not obvious at the time.
I have so advised PhaseOne, so hopefully they'll address the actual output file itself as well as the recipe profile changes.
They have so far been unable to reproduce the delay I experienced in the recipe profile drop-down window, but this has definitely only become an issue with the v9.1 update. Curiously, the directly equivalent drop-down window when selecting Proof Profile from the View menu is almost instantaneous.
Cheers,
Malcolm