How to reproduce:
1. Extract the attached project ("ResolveIssue.zip") in your prefered workspace and open it
2. Open the project, attach it to Perforce and submit it (This will be User 1)
3. Open the same project with a different user in a different workspace as well (This will be User 2)
4. With the User 1 checkout the TestFolder/test1 script and edit in a comment at line 16
5. On the User 2 project checkout the TestFolder/test1 script and add a comment at line 10
6. Submit the User 2's version of the file to the depot
7. On User 1 Get Latest and observe that the file is now conflicted
8. On User 1 go to "SimpleWindow" -> "Resolve Merge"
9. Observe that the file has no additional comment at line 10 from the User 2

Expected result: both comments from User 2 and User 1 are merged into the script
Actual result: no changes from the User 2 are merged and only the changes from the user that used Provider.Resolve are kept

Reproduced in: 2019.3.0a11, 2019.2.0f1, 2019.1.13f1
Couldn't test with: 2018.4.5f1, 2017.4.30f1

Note: Manually resolving conflicts through context menu works as expected