Upload attachments from inside 'create bill' not working

When creating a bill or an expense I am trying to upload PDF copies of the receipts, but it's not working. I am able to upload the PDFs after the bill has been saved.
System: FireFox 20.0 on Ubuntu 12.04 LTS
Steps to reproduce:

1. Create a new purchase or expense
2. Add relevant detail
3. Click 'Manage attachments'
4. Click 'Browse'
5. Select file
6. Notice that file location is listed in the box.
7. Click 'Upload'
   Result: The name of the file disappears from the box, but does not come up under 'attached files' or anywhere else.
   Once this dialogue box is closed and the bill is saved an error message appears: 'Please select file to upload'
   If you click the 'add attachment' button from this screen an attachment can be added normally.