Piwik Set Cookie multiple times in response header


I noticed some requests to piwik.php the response was really slow, some even more than 1 min (this happens randomly).
Refer to attached screenshot which shows the set cookie was done multiple time in the header.
Is the slow in response related to the multiple time of set cookie ?

Any idea why set cookie were called so many times?
The piwik is hosted in Windows 2008 IIS7.5.