Cannot create MR pipeline without merge permission to target branch

I have merge request pipelines working correctly (on Fork MRs run on the parent project when the MR creator is a parent project developer. But when the MR creator is an external contributor (not a member), I cannot manually create a MR pipeline that runs in the parent project, neither using the API nor the web UI (the button is there, but I get some error).

The target branch (master) is protected, and I don’t have merge permission, but that doesn’t prevent me from creating my own MRs and having pipelines run normally. If I give myself merge permission to the target branch, then manually creating MR pipelines works. As far as I remember, this wasn’t the case before, MR pipelines could be created by any developer with permission to run normal pipelines (not necessarily with merge permission). Has this changed recently? What is the reasoning?