I think we're all aware of the problem with round-tripping JSON

Yes, I've heard of it.
I think this is a "data serialisers" issue that dave_the_m alluded to in his last post to this thread.
There's an open perl issue about this, where changes to the way that perl's numeric flags are set/unset is being considered.
I don't know what, if anything, will come of it ....

Cheers,
Rob