hook_help's $path doesn't contain '%' wildcards.

$path in hook_help should contain '%' wildcard for paths with parameters, but it actually contains the raw path (e.g. node/1/revisions instead of node/%/revisions).

This is an example from node_help (the rest can be found with this grep -rn "case '.*%.*':"):

    case 'node/%/revisions':
      return '<p>' . t('Revisions allow you to track differences between multiple versions of your content, and revert back to older versions.') . '</p>';

so, the revisions page should contain that text, but now it doesn't.