This one blew my mind… I upgraded to Brooklyn. I have a bunch of models based on the Tasks (Activities) standard object using the “Subject” field. Prior to Brooklyn, these all rendered as text boxes. After upgrade, all these fields switched to picklists. It was like a magician pulled a rabbit out of a had. I was astonished. I assumed it was a Brooklyn issue, so I looked at the Salesforce task fields and to my amazement, the Subject field says that it is a Picklist! 
After some research, I found that the “Picklist” in Salesforce can mean either a picklist or a combobox.  The Subject field is a combobox that Skuid used to render as a text field and now renders as a picklist. I am now going through all the models and overriding the metadata on each of these subject fields to render as text.