That bug is fixed on the new jessie image scaler using 2.4.16 (tested locally, it's not yet pooled into the set of active scalers in production). I have scaled "Rsvg marker element bug.svg" on the new and the present image scalers and put the results at https://people.wikimedia.org/~jmm/svg/ :
new-arrow.png is the result on the jessie scaler
old-arrow.png is the results with an existing scaler
(The pixel sizes differ slightly to prevent hitting the cached results in favour of a fresh scaler run)
@Menner, @Tgr: Fixed. For confirmation I have re-triggered the generation of File:Rsvg marker element bug.svg five times and it was always rendered correctly. The reason that it partly returned the old version, was an oversight on my side; some of jessie scalers were still using the standard version of librsvg as shipped in Debian jessie, as some of the servers had been installed prior to the upgrade of librsvg. All new image scaler installations will use the new librsvg from the start.