Steps to Reproduce

1. As an administrator create around 10 groups for testing purposes
2. Ensure 'Comment Visibility' in 'General Configuration' is set to 'Groups & Project Roles'
3. Navigate to the Detail View of an issue and click on the 'Viewable by..' drop-down list
4. Resize the browser screen so that only a portion of the Groups drop down list are shown (for testing purposes)
5. Compare this behaviour with standard View Issue page

Expected results

The Comment Visibility drop-down list in Detail View should be scrollable like Issue View

Actual results

The Comment Visibility drop-down is cut off in detail view and is not scrollable

Temporary Workaround

Maximize the browser in the window, and zoom out in browser settings (will vary depending on browser) until the whole list is shown.
Generally to zoom in/out:
Windows - (CTRL +/- )
Mac: - (CMD & +/- )