On the latest release of OnDemand, the post-function:

"The Resolution of the issue will be cleared." 

Is being displayed as follows:

Type: class
Class: com.atlassian.jira.workflow.function.issue.UpdateIssueFieldFunction
Arguments:
field.value =
field.name = resolution

There is a screenshot attached to better understanding.

The post-function is executed correctly, it is only the UI that is having problems.

Also, it is not possible to edit, delete or move down the post-fuction, as it was possible on the previous versions. To delete the post-function from the transition, the transition must be entirely recreated.

Haven't been able to replicate this on JIRA Standalone 5.1.6