Resolve merge command blows away entire file, irrespective of conflicts

The “Resolve Conflicts > Resolve Using {Mine|Theirs}” commands in SourceTree do not behave as expected. Rather than resolving conflicts according to the selected side, it seems that the ENTIRE FILE is replaced by either “mine” or “theirs”.

As a user, I expect that the successfully auto-merged chunks remain intact (as they first do prior to conflict resolution). Instead, they are unexpectedly reverted.

Verifying this bug has been made more troublesome by the fact that SourceTree does not log in its command history panel what it's actually doing when I choose a resolve command.

The current behaviour renders the “Resolve Conflicts” command mostly useless (and indeed dangerous), making a manual treatment (by editing the text of the conflicted merge product) the only way to achieve the correct merge.
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