On editing a ticket the entry text area remains. I assume this is to allow for multiple edits which is fine. However the preview area still reflects the previous change so needs to be cleared on Submit.
And sorry this ticket was posted to docs-en, you can move it to the proper project.
sado 
OSDN Docs (English)
When editing a ticket or submitting a comment the preview area remains populated on submit of the ticket. The Submit button is below the preview area. This makes it seem that you can resubmit the previewed text more than once when in fact you would submit an empty ticket or comment because the entry area is empty.