Unmerge and Collaboration Items
It has been my experience that when an unmerge of records is initiated, the items found under the Collaboration tab remain with both records. This causes confusion since the purpose of the unmerge is to cause separation and distinguish differences between the two records in question. The only option available at this point to complete the unmerge is to physically delete the items individually. My suggestion is to attach the Collaboration items to their original record, so that when an unmerge occurs the Collaboration items only follow the original record and are automatically deleted from the merged record.