Nondeterministic recoloring of symbolic icons

When gtk-encode-symbolic-svg converts a symbolic SVG into a PNG, sometimes one or more of the success/warning/error colors is missing and the areas remain uncolored (black).

I've extracted one of intermediate SVGs it produces: plane-1.svg.

Rendering this file using rsvg-convert is similarly nondeterministic, producing either of the following outputs:
Correct:
Broken: