Comment 1 for bug 449923

bzr merge validates that the diff is a true representation of the requested change, by generating its own diff and ensuring it matches. Changing the format of the diff in bzr send would make the diff fail validation.

Using --diff-options also causes an external program to be invoked, which may have output variations across different platforms, so that even if the same diff options were applied when merging, the chance of a spurious validation failure is higher. Providing metadata to reproduce the diff options would likely require a new merge directive format.