I think it is a combination of two things: - the mod-256 conflict bug is exceedingly rare. Keep in mind that this is mod-256 individual hunk conflicts in a _si

I think it is a combination of two things: - the mod-256 conflict bug is exceedingly rare. Keep in mind that this is mod-256 individual hunk conflicts in a _single file_. Most files in a merge with conflicts have a handful of hunks. Over all of the testing at GitHub, only a single merge triggered this bug, and it was on a long repetitive file with automated changes. - the failure case was to quietly accept the merge. The result was obviously bogus, but didn't look any different than a user accidentally checking in the merge conflict markers. So if it was happening, I'd suspect that it went undiscovered either because the merge results were never used (e.g., it was a test-merge to feed the PR "Merge" button status) or the users simply scratched their head and fixed it.