MNTP gives "TypeError: $scope.model.value.split is not a function" when clicking "Select" button

Questions
1

I have this property:

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When using the property on a document type the CMS editor can´t use the property since it gives this error:

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Have anyone experienced that and found a solution?

This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/108454-mntp-gives-typeerror-scopemodelvaluesplit-is-not-a-function-when-clicking-select-button