Uploads not working in composer field

Environment

Discourse Version: tests-passed

Plugin Commit: latest

Other Plugins
thepavilion.io plugins

Steps to Reproduce

  1. Add a composer field to a wizard
  2. Upload at least one (or multiple images)
  3. Upload (sometimtes) fails. It seemed to have worked this time, but the previous bug report produced this error:

Example

http://thepavilion.io/w/bug-report

Logs

@angus uploads seem to be working for me.