Cannot add a custom text renderer plugin

I developed a simple text renderer that does nothing more than wrapping the comment text into <pre> tags. The renderer is correctly recognized by JIRA.

However, when I want to change the comment field to use the renderer, I get the following error:
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Errors
"Tried to add a renderer type: fixed-text-renderer that is not know to the system.
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Steps to repeat (fresh install):

• Copy plug-in (attached to this bug report) into edit-webapp/WEB-INF/lib
• Build, deploy & start server
• Complete setup wizard
• Log in as admin
• Go to Administration -> Field Configuration
• Click on 'Configure' for the default configuration
• Click on 'Renderers' for the comment field
• Select 'Fixed-Width Text Renderer' and click 'Update'
• Confirm update
  => Error