When multiple collaboration items are created (for example, using the approval workflow) and the 'frequent' cronjob is executed, the first collaboration item's participant list is incorrectly used in the remainder of the collaboration items.

The culprit seems to be eZCollaborationItemParticipantLink::fetchParticipantList() returning incorrect/"cached" data.

Steps to reproduce

• Create two collaboration items with different users (for example, using the approval workflow)
• On both users, enable collaboration in notification settings.
• Run the "frequent" cronjob.

Result:

• The participant list of the second item is incorrect (it's actually a copy of first item)
• the user editing the first item will receive both notification emails.