Dragging and dropping files on transition screen results in duplicate attachments

Issue Summary

This is reproducible on Data Center: yes

Steps to Reproduce

1. Add a new screen containing the Attachments field
2. Associate the new screen with a transition in any project's workflow
3. Transition the issue to trigger the new screen
4. Drag and drop a file into the attachment area

Expected Results

One copy of the file is attached.

Actual Results

Two copies of the file are attached. The following REST endpoint is being called twice:

rest/internal/2/AttachTemporaryFile 

Workaround

Upload files using the browse option instead of dragging and dropping.