Non-deterministic behaviour of MultiZarrToZarr

I'm seeing what looks like non-deterministic behaviour with MultiZarrToZarr. It happens both with and without writing to parquet. Sometimes I get the expected result written, sometimes I don't. See the standalone notebook here.

I'm also seeing different behaviour when I do/don't write out to parquet. Even the act of writing to parquet is changing the json returned by MultiZarrToZarr.

(The example in the notebook comes from a snippet I created whilst trying to work around the bug reported in #386 - see https://github.com/fsspec/kerchunk/issues/386#issuecomment-1979532213. It's slightly odd because I preprocess then postprocess in the same MultiZarrToZarr call. But that should be a perfectly well-defined thing to do.)

This behaviour might be specific to the application of preprocess and postprocess, but it also might be indicative of a more wide-reaching bug.

I am hoping I am somehow using MultiZarrToZarr incorrectly, but given how I'm running identical code in consecutive cells and seeing different behaviour, I don't understand how this can be user error.

Start with the standalone notebook linked in the issue and reproduce the consecutive MultiZarrToZarr calls, both with and without parquet output. Compare the returned JSON and generated results when using preprocess followed by postprocess; done means identical code produces deterministic, expected output in both cases.