MIME type issues with "drag and drop" upload method in certain browsers with Confluence 3.5

Steps to reproduce:

1. Using either Firefox 3.6, 4.0, or Chrome, upload an .xlsx document to a page via drag-and-drop
2. In the database, the contenttype column of the attachments table will store "application/vnd.openxmlformats" instead of the intended "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"

Please note that the same browsers using the "select file + upload button" method correctly populates the contenttype column with "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet".

Internet Explorer 8 is not affected by this bug and correctly populates the database with either upload method.

Seems to be a variation of the following, except not involving Google Gears but instead HTML5:
https://jira.atlassian.com/browse/CONF-18580