When exporting a search to excel in issue navigator, not all columns are exported.

Steps to reproduce

1. create a custom field
2. make it available for two issue types (bug, improvement for instance)
3. create some issues and populate this custom field
4. now, perform a search on the issue navigator: 'project = X' for instance
5. add the custom field as a column on the issue navigator
   make sure the column is being displayed
6. export to excel (current fields / all fields)

Expected behaviour

custom field is exported as well

Actual behaviour

the custom field is not exported

Workaround

1. change the search on the issue navigator to include the issue types the custom field is available for: 'project = X AND issuetype = Bug'
2. export to Excel (current fields) one more time. Now, the custom field is exported