The following appears within the cron output on a site using this block:

• Processing cron function for grade_me....

  INSERT

  INTO {block_grade_me} (

  SELECT

  gi.id `itemid`

  , gi.itemname `itemname`

  , gi.itemtype `itemtype`

  , gi.itemmodule `itemmodule`

  , gi.iteminstance `iteminstance`

  , gi.sortorder `itemsortorder`

  , c.id `courseid`

  , c.shortname `coursename`

  , cm.id `coursemoduleid`

  FROM {grade_items} gi

  LEFT JOIN {course} c

  ON gi.courseid = c.id

  LEFT JOIN {modules} m

  ON m.name = gi.itemmodule

  INNER JOIN {course_modules} cm

  ON cm.`course` = c.`id`

  AND cm.`module` = m.`id`

  AND cm.`instance` = gi.`iteminstance`

  WHERE gi.`itemtype` = :itemtype

  AND m.`name` IN ('assignment','data','forum','glossary','quiz')

  ORDER BY gi.id

  )

  ON DUPLICATE KEY UPDATE

  `itemname` = VALUES(`itemname`)

  , `itemtype` = VALUES(`itemtype`)

  , `itemmodule` = VALUES(`itemmodule`)

  , `iteminstance` = VALUES(`iteminstance`)

  , `itemsortorder` = VALUES(`itemsortorder`)

  , `courseid` = VALUES(`courseid`)

  , `coursename` = VALUES(`coursename`)

  , `coursemoduleid` = VALUES(`coursemoduleid`)

  Updated block_grade_me cache in 0.642211 seconds

This is from version 4.0 (Build: 2012080500) running on a 2.2.4+ site. It's probably happening in other versions, though, as well.