Diffusion is showing unexpected diffs for commits in which an entire directory is removed. See rP5c1e4488dedafda08684b33a8a4786cf687d2811 for example, in which the src/infrastructure/daemon/bot directory was deleted:
(For rP5c1e4488dedafda08684b33a8a4786cf687d2811, the "diff" shown for src/infrastructure/daemon/bot is actually the diff for src/infrastructure/daemon/bot/PhabricatorBot.php)
I often see this bug on our Phabricator installation as well.