OJS Custom DOI pattern requires article to be assigned to an issue

Describe the issue or problem
If our journal uses a custom DOI pattern (in all of our cases, the journal initials followed by %a), you get the following error message when assigning a DOI to an article that has not yet been assigned to an issue:

‘The submission must be assigned to an issue before a DOI can be generated.’

This despite the custom pattern not using an issue number.

What application are you using?
For example, OJS

Has anyone else experienced this and found a fix?