@Dušan, the authorities in Bosnia and Herzegovina at the time had little desire to keep the Poles around plus Poland was embarked on a policy of repatriation. You combine that with a bit of terrorism (like what happened to Polish civilians in Bosnia towards the end of WW2) and the numbers evaporate quickly. I know all about Prnjavor. My mother grew up there in her youth and it is(was) very multi-ethnic seeing as how she had Czech and Rusyn grandparents in Prnjavor :).