I was trying to build the java-driver myself. So I pulled it from github and switched to the r2.12.1 tag.
When I try to build it, the testUTF8 test in the BSONTest-class fails. This happened on a windows machine, so I thought there might be a problem with some weird windows specific encoding. So I tried the same on a current ubuntu machine. Same result. I looked at the test. And it is looking through all possible code points. When I altered it to just print the numbers it is failing for and not stop at the first, it fails 2047 times, starting with 55297 till 57343.