Ah, yes. That does help.
It seems to confirm that the "eat your own dogfood" approach gave us
100% icon fidelity, whereas splitting things out to other rendering
libs. holds us to problems with their implementation/compatibility
The one other thing that might help is if you check using Batik. That
can help point out which ones are hitting bugs in Inkscape vs. which
ones are hitting limitations in librsvg.
Thanks for investigating.
Batik-squiggle does indeed display the icons correctly.