Clearly some weird historical configuration that has got messed up. I've searched everywhere to try to find where to turn this on, the setting has eluded me so far.
Where on earth is this setting hiding?
Resolved.
Project Settings > Permissions > Actions > Edit Permissions > Turn on 'Add Comments'
What a daft place to put this setting.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.