I don't necessarily disagree with most of you, but I believe it is more important to manage different species correctly, once that is done the problems are greatly reduced.
I have had Zebras, Javas and Shaftails in one aviary and successfully bred all of them at the same time with no problems. I believe having incompatible species and odd numbers of one species, especially a pushy species, greatly increases problems, but when you have bonded pairs they tend to concentrate more on their own breeding than harassing other birds.
My setup was working great until I added star finches to the mix, there still wasn't much fighting but the stars are to small to defend their nests and were chased off by the Zebs, the same happened when I added my BCCB.
I have now removed all Javas and Zebras and the odd shaftail (my other pair is breeding) into their own aviary and peace was once again restored.
The compatibility chart is not the alpha and omega of finch keeping but I believe it is there for a reason and should be adhered to. I am not arguing that certain personalities occur in birds and in some cases seemingly incompatible birds can be kept together, but 90% of the time it will work if you stick to the compatibility chart.