Milestones count merged MRs as closed issues when determining progress
When accepting a merge request that is associated with a milestone, it counts towards the "closed" count of that milestone. However the progress is determined by closed_issues/total_issues, as it should. The total issues consists only of "real" issues, not merge requests, as it should. Therefore completion measuring is inaccurate when merge requests are involved. (See screenshot below)
As this screenshot shows, there are 5 total issues in this milestone, 4 are open and 2 are closed. The 2 closed here are a regular issue and the merge request that closed that issue.
Merge requests should not count as "issues" as far as a milestone is concerned.