Randomisation does not work in Parson's block when ordinals are used as proof_steps tags

[smmercuri]

When writing Parson's problems, using ordinals as the tags, and randomising in the Question Variables field as:

proof_steps: [
    ["1", "<proof step one>"],
    ["2", "<proof step two>"],
    ...
    ["n", "<proof step n>"]
];
proof_steps: random_permutation(proof_steps);

Proof steps are still displayed in order on the question page, so randomisation seems to have no effect. This is only an issue for ordinal tags; for any other tags randomisation still works.