The order of filters matter here, just need to apply lowercase token filter before removing stopwords
result = new StopFilter( result, stoptable );
result = new BrazilianStemFilter( result, excltable );
// Convert to lowercase after stemming!
result = new LowerCaseFilter( result );
Lowercase must come before BrazilianStemFilter
At the end of day I'll attach a patch, it's straightforward