I have identified the cause of the issue. Apparently, if the clientlib as defined in the step 2, 3, and 4 of the solution, presented in Experiencing Adobe Experience Manager - Day CQ: AEM 62 - Touch UI Composite Image Multifield exists more than once in the repository, that will cause the author dialog of each instance of the component, to have multiple image drop areas equal of the total number of occurrences of the above clientlib. The issue is not only visual, but also functional.
After removing all duplicates from the repository, my Touch UI Composite Image Multifield works fine again.
I hope that helps to all who have faced the same issue.