As described in the release notes: https://www.apache.org/dist/commons/bcel/RELEASE-NOTES.txt, this release contains the followings:

Experimental Java 9 Support.

FIXED BUGS:
===========

o BCEL-294: Incorrect comment in StackMap.java Thanks to Mark Roberts.
o BCEL-296: Incorrect comment in several classes. Thanks to Mark Roberts.
o BCEL-295: Fix local variable live range length; add test case. Thanks to
Mark Roberts.
o BCEL-300: org.apache.bcel.classfile.ClassFormatException: Invalid byte
tag in constant pool: 19.
o BCEL-301: org.apache.bcel.classfile.ClassFormatException: Invalid byte
tag in constant pool: 20.