Correct, 
Unlikely, `xbs2` is not empty, if you see my the commits, I added it for

+Failed 3 tests: 
+ ../benchmarks/bytestring-0.9.2.1/Data/ByteString.split.1.T.hs,
+  ../benchmarks/bytestring-0.9.2.1/Data/ByteString.split.1.hs,
+  ../benchmarks/text-0.11.2.3/Data/Text/Foreign.hs 

If you have a more elegant solution, it is wellcome