Some metrics show higher values for CustomVariable subset data than in general

I get a higher value for metrics like “nb_visits” and “nb_actions” with a CustomVariable than for general analytics, how is it possible?
Here are my API calls and their results:

  • query 1: http://…/piwik/index.php?token_auth=…&idSite=82&module=API&period=range&date=2013-03-25,2013-04-15&method=API.get&format=JSON

  • result 1: {“nb_uniq_visitors”:26,“nb_visits”:18,“nb_actions”:234,“max_actions”:43,…

  • query 2: http://…/piwik/index.php?token_auth=…&idSite=82&module=API&period=range&date=2013-03-25,2013-04-15&method=CustomVariables.getCustomVariables&label=UserId&format=JSON&expanded=1

  • result 2: [{“label”:“UserId”,“nb_visits”:72,“nb_actions”:904,“max_actions”:55,…

So this would mean that I have more visits from user accounts than the total number of visits? And user accounts have produced more actions than the total number of actions?

Can you replicate this on the ?