Occours in https://commons.wikimedia.org/wiki/File:Labanotation2.svg and in https://commons.wikimedia.org/wiki/File:Nixie_IN17.svg:
In https://commons.wikimedia.org/wiki/File:T194582_filter.svg the filter is not applied: (number 9 looks different than 0)
<path filter="url(#a)" transform="matrix(-.197 0 0 -.197 474.15 222.85)"/>
In https://commons.wikimedia.org/wiki/File:T194582_href.svg it doesn't blur the twice mirrowed path: (some path are not blured)
<use transform="matrix(-1 0 0 -1 0 0)" xlink:href="#a"/>