Visits from external Websites not being counted

Hi, I just noticed that some visits via external websites were not counted by Piwik:

$ grep “piwik/piwik.php.*twitter.com” access.log.1 | wc -l
7

here’s one example line from access.log.1:

      • [12/Dec/2009:14:26:13 +0100] “GET /piwik/piwik.php?idsite=1&url=http%3A%2F%2Fwww.my-example-site.de&res=1024x600&h=14&m=26&s=8&cookie=1&urlref=http%3A%2F%2Ftwitter.com%2F&rand=0.21140252271541626&pdf=1&qt=1&realp=0&wma=1&dir=0&fla=1&java=1&gears=0&ag=0&action_name=whatever HTTP/1.1” 200 43 “www.my-example-site.de” “Mozilla/5.0 (Windows; U; Windows NT 5.1; de; rv:1.9.1.5) Gecko/20091102 Firefox/3.5.5 (.NET CLR 3.5.30729)”

However, twitter.com does not show up in any “external Website” referers, and I can find no trace of it in the Piwik database.

Besides the missing twitter referrals, there is at least one other example of links that weren’t counted.

This this a known problem? If not, can I help track this down?