Concurrency problems with enum constraints in MVEL

Having a test case like this [1], it sometimes fails on
java.lang.RuntimeException: java.util.concurrent.ExecutionException: [Error: unable to resolve method using strict-mode: org.drools.compiler.integrationtests.facts.FactWithEnum.AnEnum()]
[Near :

]
... see here [2]. When using direct imports that are commented out in the pasted example, I see very rarely also a ClassCastException. See stacktrace here [3].
Tested with mvel 2.2.8 on 6.5.x branch, 2.3.0 and 2.3.1 on master branch.
[1] https://gist.github.com/baldimir/d0f5f21d5b1a383887c5ebfb6013e5af
[2] https://gist.github.com/baldimir/da5c9cb23fab2eae1576948c8ca2a4c8
[3] https://gist.github.com/baldimir/72eafe3909c21e25265cd3ee9a731d8e