Kanban backlog Fails to install during upgrade when dark feature is enabled

Summary

If you have enable the Kanplan Dark feature to test the feature in JIRA 7.3.X and upgrade to 7.4.0 while the darkfeature is enabled the Kanban backlog feature will fail to install.

Instruction to enable experimental dark feature visible to public in various locations i.e.:

• https://community.atlassian.com/t5/JIRA-questions/jira-kanban-backlog-on-server/qaq-p/154388

Environment

• JIRA Software 7.3.X Upgrading to 7.4.0+
• com.atlassian.jira.agile.darkfeature.kanplan set to Enabled

Steps to Reproduce

• Install jira 7.3.x
• Navigate to BASE_ULR/secure/SiteDarkFeatures!default.jspa
• Enable com.atlassian.jira.agile.darkfeature.kanplan
• Upgrade to 7.4.0
• Attempt to Enable the backlog as covered here

Expected Results

Enable backlog option is available

Actual Results

The option to enable kanban backlog is missing, and cannot be enabled

Workaround

Disable the dark feature before upgrading

OR Roll Back To 7.3 and then disable the dark feature and re-upgrade to 7.4.0