Refer to release notes at:
https://www.apache.org/dist/commons/bcel/RELEASE-NOTES.txt

BCEL 6.1 contains:

NEW FEATURES:
=============

o BCEL-293: Add Automatic-Module-Name MANIFEST entry for Java 9 compatibility.
o BCEL-292: Add minimal Java 9 support.

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

o BCEL-286: Utility.signatureToString fails if a method has multiple type arguments.
o BCEL-287: IINC does not handle -128 properly.
o BCEL-283: Support for StackMap should be different from StackMapTable.
o BCEL-289: Crash when parsing constructor of inner classes with parameters annotated.
o BCEL-276: LocalVariableTypeTable is not updated.
o BCEL-277: Resolving the String representation of a constant throws NoSuchElementException in case of CONSTANT_NameAndType constant.