Unable to use jackson within custom score scripts

I am upgrading from ES 1.7 to 2.3.1 but I'm not able to get my custom score scripts running. they have complex DTOs as parameters that's why i use jackson to deserialize the string parameter within my Java score script.

I tried 3 different ways:
add jackson within the plugin folder: java.lang.IllegalStateException: jar hell! during startup
add jackson within the plugin.jar: java.lang.IllegalStateException: jar hell! during startup
add no jackson jars: java.lang.ClassNotFoundException: com.fasterxml.jackson.databind.ObjectMapper during script call

I also tried to change the isolated property in the plugin-descriptor to false => same results for the 3 ways above

If I remove the jackson imports and initialize the parameter DTOs with hardcoded values, everything works.

Any ideas what I do wrong?
ES=2.3.1, jvm=jdk1.7.0_79, OS=windows 10, jackson-version=2.6.2 (the same as ES 2.3.1)