Select Multiple Items in Drop-Down Box

I am trying to build a drop-down box within Excel that allows for multiple selections. I was able to use some code provided by Contextures (http://www.contextures.com/excel-dat....html#Multiple) to do this. The one addition I would like to make is to also allow users to type in values in addition to being able to choose from the drop down list. However, whenever this code is used in conjunction with allowing users to type in their own responses, the code somehow causes the entry to duplicate the prior entry. For example, if the user selects "Apples" and "Oranges" from the drop down list, the cell will display, "Apples, Oranges". However, if the user now types in the response "Bananas", the cell will now display "Apples, Oranges, Apples, Oranges, Bananas". The way the code is set up, it is somehow copying the original value, and just inserting it before the new value. I'm not sure how to correct this so that the end product only reads "Apples, Bananas, Oranges".

Any suggestions? I've pasted the code I'm using below.

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