Merge conflicts cannot be resolved if both users commit and one of them pushes.

To reproduce this behavior:
1) user A performs a change on a line of a SP
2) user A commits and pushes
3) user B performs a change on the same line of the same SP
4) user B commits
5) user B tries to pull and a message says conflicts must be resolved outside SQL Source Control and it is also impossible to push (please see the attached screenshots)

Only if user B performs step 4 after step 5 it is possible to see the conflict resolution bar and use an external merge tool (clicking on the merge button).