"unexpected individual metadata length" when remapping subpopulations

[petrelharp]

With this tree sequence: fox.zip (note, this is just a .trees file, renamed so I can upload), this script:

initialize() {
    initializeSLiMModelType("WF");
    initializeTreeSeq();
    initializeMutationRate(1e-2);
    initializeMutationType("m1", 0.5, "f", -0.1);
    initializeGenomicElementType("g1", m1, 1.0);
    initializeGenomicElement(g1, 0, 99);
    initializeRecombinationRate(1e-2);
}

1 early() {
    sim.readFromPopulationFile("fox.zip");
    sim.readFromPopulationFile("fox.zip", subpopMap=Dictionary("p1", 0));
}

errors out with

ERROR (Species::__RemapSubpopulationIDs): unexpected individual metadata length; this file cannot be read.

Error on script line 13, character 8:

    sim.readFromPopulationFile("fox.zip", subpopMap=Dictionary("p1", 0));

Note this happens only if subpopMap is specified. This happens here, and I don't see what's wrong with the code? The metadata is in fact fine, as far as I can tell (and the fact that it is read in fine without the subpopMap argument supports this).

[bhaller]

I think I probably know why this is happening? I'll look into it, thanks!