When you disable a user in Active Directory and the user is part of a K2 Role, enabling the user at a later stage causes a problem in the K2 Role membership. For example, the user will not be able to open worklist items when the K2 Role was used as the destination user.
After installing this fix pack, you need to sync the users again in K2 Management. This is only required the first time after installing the fix pack. After that disabling and enabling users will work as expected and not remove the users from the K2 Role.