Why are 2 RTC work items in separate RTC project areas created with the same work item ID?

We are currently on RTC 6.0.1.  We have noticed 2 work items with the same work item ID 62336 have been created.  I am under the assumption that every work item ID is unique.  They are in 2 different project areas.  Work Item A is a custom work item type and Work Item B is a story work item.  When performing searches in top right corner, this leads to being directed to Work Item A. Work Item A was created July 9, 2017 and Work Item B was created one day later on July 10, 2017.  Any reasoning why these two work items were able to created with the same ID?