This will be fixed in version 1.9.2 of Infinity. This is expected to be released next week. Be warned that 1.9.1 will remove Thaumic Horizons.
I assume you mean it's being removed in 1.9.1 but being fixed and put back in on 1.9.2... can you confirm? Also, will this fix correct worlds that already have portal biomes in them? Thanks!