FieldMesh saved cannot be reopened

[ColwynGulliford]

I have several FieldMesh h5 files generated by Bmad via write bmad. When loading these maps into Python via FieldMesh initialization for the first time, there is a warning:

Nonstandard attr: componentFieldScale [1.]
Nonstandard attr: interpolationOrder [1]

Saving a new map via FieldMesh.write(...) and then trying to reload the new map causes an error:

Attached is a minimal working example using a Cornell injector solenoid field map file.

pmd_mwe.zip

[ChristopherMayes]

@ColwynGulliford could you add the Bmad file that makes this? I can't reproduce.