Vocoder carrier wave bleed
I have, since my troubles with vocoders, learned a lot about signal processing in school and gone back to revisit some of my older projects and fix them. The problem with my vocoder implementation was that I was defining bandwidths in octaves, but linearly spacing my filters. There would be more overlap in higher frequencies and less overlap in lower frequencies. I'm not sure how I got carrier bleed, perhaps a bad envelope follower, but re-implementing with better filters was the real solution.