Thanks Jozef for bringing this to dev@ and your work in reporting Jiras and offering fixes.
I propose we consider BEAM-5180, BEAM-2277 blockers on 2.7.0. They break word count and file IO writing on HDFS unless the workaround is used (see BEAM-2277 commentary).
In addition the performance of writing to HDFS is bad (to the point of being unusable) due to BEAM-5036 (blocked by BEAM-4861) which you have also observed. I don’t think we’ll make the cut for 2.7.0 on those because I anticipate significant testing is needed. I will focus on that as soon as I have time but I propose we make those blockers on 2.8.0 though.