I recently ran into a pretty nasty bug in KeyBuilder[1]. If a CharSequence greater than 9 characters is used in any of the KeyBuilder methods, the charset encoding will pad the end of the value with an empty byte. This can be very difficult to detect since activities across Accumulo can silently fail or lead to unexpected results in your data. I already pushed a fix for the main branch (version 2.1.0). This bug exists in 2.0.0 and 2.0.1 so this may warrant a 2.0.2 bug fix release.
[1]: https://github.com/apache/accumulo/pull/2170
