Hidden field doesn't preset value during customer request creation

Summary

Hidden fields that can't be shown on the Customer Portal, doesn't set the default value when request is created by customers.
These type of fields are displayed with the "Show" option greyed out under Service Desk "Request Types" section.
Hovering over the "Show" option displays the message: "This field type can't be displayed in Customer Portal"
e.g fields: Epic Link, Assignee

This affects Issues Created by the Customer Portal as well as Email

Step to Replicate

1. Under a Request Type configure the screen and add Epic Link as a hidden field.
2. Set the default value of the Epic Link to an existing epic link.
3. Login as a SD Customer (or create a new one for testing purposes); raise a request with the above request type.
   Expected Result: Epic Link field is set to the default epic link and shown at JIRA ticket view screen.
   Current Result: Epic link field is empty and thus not showing on the JIRA ticket view screen.

Notes

The problem doesn't affect agents.
The event that sets these fields requires edit permissions for the field and so it fails when Customers don't meet those requirements.

JIRA logs the following warning:

2015-08-26 10:19:06,507 Caesium-1-4 WARN email@address.com     [c.a.jira.ofbiz.ConnectionPoolHealthSqlInterceptor] Dangerous use of multiple connections: taken => count=3; marks=[3-3]; pool=3/-1
java.lang.AssertionError: Explicit stack trace requested
      at com.atlassian.jira.util.log.RateLimitingLogger.warnWithTrace(RateLimitingLogger.java:163)
...