'Assign To' issue field cannot be set in workflow postfunction

In our workflow we have added an extra postfunction to the 'Create Issue' transition. In this function we set the 'Assign To' issue field to a specific user. This is done to have all Feature Requests processed separately. This used to work fine in 3.0.3, but in 3.3 JIRA is checking if the user that created the Feature Request does have the assign issues permission (according to this stacktrace):

Caused by: com.atlassian.jira.workflow.WorkflowException: Error occured while creating issue.
at com.atlassian.jira.workflow.SimpleWorkflowManager.createIssue(SimpleWorkflowManager.java:174)
at com.atlassian.jira.issue.managers.DefaultIssueManager.createIssue(DefaultIssueManager.java:303)
... 60 more
Caused by: com.opensymphony.workflow.WorkflowException: Unable to execute post workflow function. Issue may be in an inconsistent state. Please inform your system administrators immediately. Validation of the field 'assignee' failed: [You do not have permission to assign issues.] {}
at com.atlassian.jira.workflow.function.issue.UpdateIssueFieldFunction.processField(UpdateIssueFieldFunction.java:185)
at com.atlassian.jira.workflow.function.issue.UpdateIssueFieldFunction.execute(UpdateIssueFieldFunction.java:110)
at com.opensymphony.workflow.AbstractWorkflow.executeFunction(AbstractWorkflow.java:1179)
at com.opensymphony.workflow.AbstractWorkflow.transitionWorkflow(AbstractWorkflow.java:1434)

It seems to me that performing a postfucntion in a workflow transition is something the JIRA system is doing and not the user that is creating the issue. For obvious reasons we don't want to give everyone the assign issues permission.

(I noticed some problems with other fields as well. It looks like setting the value for the Priority is broken as well, maybe due to permission issues too.)