Have you disabled them and or the OSD?
Every time I start a DVD that has different subtitle options VLC goes nuts and tries to build a font cache, it gets very frustrating, you sit down bag of m&ms in hand start a film and then by the time the font cache is finished being built the m&ms are gone! Very frustrating! Not only that I don't want the subtitles anyway.
I've seen this before, you can't even operate VLC until it renders the fonts so disabling them doesn't help at this point.