probabily I didn't explain well
the context is apply a SLD to mapfile
the anomaly rise up due the fact that Mark symbol are shown in mapfile but the svg symbol not
In fact for Mark symbol, the symbol->inmapfile  is set to true

mapogcsld.c:1747 - msSLDGetMarkSymbol

I'm agree that, with your explication, symbol->inmapfile = MS_TRUE shouldn't be in msAddImageSymbol, my idea is this should be done at the level of  parsing the sld.