Two collector type fields are being shown differently in a report. One seems to expect a string input while the other one shows a drop-down choice type. 

In the dictionary of a colletor type field if you make the choice field "Dropdown with -- None --" it will show this field as a choice drop-down in a report. For example, if you make the watchlist in the incident table as a choice field "Dropdown with -- None --" it will show the field in a report as the following image attached below. This is compared to the "work note list" field.

Change the choice to none if you want to input strings.