When trying to update variable within a repeat param step that is parallel, the steps override each other.
e.g. if the parallel step is:

groovy:
vars.get("test").setValue( " " + vars.getValue("test") + params.get("name").toString() )

with Repeat Parameters 1,2,3,4
the value of test will be randomly one number between 1-4, instead of 1234 in random order.