Form checklists get "cannot be assigned to TEXT" error

Among the items on my form I have several checklist widgets, with values bound to JSON form variables. I've found that whenever I try to select anything on the checklists, the form won't submit - the error explanation on the Engine Log looks like:
[Victoria, Prince George, Burnaby] cannot be assigned to TEXT{lName=Smith, newUserRequestor=Jane Doe, endDate=null, jobTitle=null, fName=John} cannot be assigned to COMPLEX type
This error hasn't come up when I use other types of widgets, including dropdown lists and radio lists.
All of the checklist items are text type instead of strings in my BDM, just in case enough items are selected to exceed the character limit, as is possible with a few of them.
The contract isn't the issue, and I've kept my formInput and formOutput updated too... Unless I need a specific formOutput function for checklist types?
Are there certain characters that shouldn't be returned in the text (besides "\")?