Well, I guess this conversation will have to continue in public. Caleb, if you want to take advantage of the fact that my blog supports followup comments, please feel free.
Thank you for clarifying what you meant with respect to “id” vs “in”. I though that the “id” attribute in question was on the ‘filter’ tag rather than the feGaussianBlur tag. The former seems to be a non-negotiable attribute while the second can, as you say, be done without. If I was aware of this at the time, I’d certainly have immediately made that change, or discarded the attribute completely, but as I thought the offending id was the ‘filter’ id, the only way to avoid the problem was to remove the gaussian blur, and that was the precedent that I didn’t want to set. I certainly have no objection to tweaking the file without affecting the artwork, and I should go do that right now! It would have saved us much grief if we’d been aware of it at the time.
I wondered to myself whether the first blog entry was belabouring the point, and clearly it was. I did not, and do not, want to create the impression that you and the rest of the librsvg team are not responsive; My apologies.