as Mike Burton already pointed out  there is an issue with Java 8 (possibly interaction with eclipse).
$mvn dependency:tree shows that there are two versions included via:
javassist:javassist:jar:3.12.1.GA <- org.reflections:reflections:jar:0.9.8
org.javassist:javassist:jar:3.18.1-GA <- isis-core-unittestsupport, isis-core-metamodel
According to , 3.18.2-GA should work with Java 8.
 shows that reflections 0.9.9 uses 3.18.2 as well.
Please update the dependencies if possible.