When the 'Copy Field Value to Parent ' post-function is set on a Sub-task workflow transition for a custom field (on my test case it was a 'Multi Checkboxes' field type), the sub-task's custom field value is correctly reflected on the 'Issue Navigator' when performing a query parsing the custom field value.
While the sub-task's parent custom field value is not directly reflected on the 'Issue Navigator'. Only after performing a 'Lock JIRA and rebuild index' it is updated. Not even the 'Background re-index' is effected.

Steps to reproduce:

• Add a custom field to a screen.
• Add the 'Copy Field Value to Parent' post-function to a workflow transition that is applied to the sub-task (on my test case it was from 'In Progress' to 'Close').
• Add the 'Clear Field Value ' post-function to the same workflow transition for the same custom field, and place it above (to be executed first) of the 'Copy Field Value to Parent' post-function.
• Create an issue (parent) populating the custom field.
• Create a sub-task for this recently created issue, populating this custom field with a value.
• Make the workflow transition, so the above post-functions can be executed.
• Perform a query on the 'Issue Navigator' for the custom field value that was populated when the parent issue was created (it should be cleared now, and it is, but the index for the parent issue was not successfully built)