Because I don't really know if it's a bug on whose side, I decided to at least put in the issue via this list.
When I try to load the VOC dataset using the JdbcClient with the new -Xbatching flag, the client hangs when it wants to send its last batch. I'm batching in chunks of 8000 statements. Research pointed out that the Java streams are trying to write data to monet, but it simply can't write it, and locks. I pinned down the problem to be in the very low level code regions which are outside of the Java reachable scope and go into the level of the operating system. It just cannot write to the stream.
Monet on the other hand seems to be waiting for data. When I use a smaller dataset the batching goes fine.
Any clues on what to look for? GDB couldn't help me out much.