Issue:
Office 2010, IE 9 - IE10, SharePoint Online (SPO O365), when a user clicks on a document in a SharePoint document library two instances of the office application are stared. Two windows showing the same document are opened by the single click in the document library.
Workaround:
**This workaround does have some side effects, you lose the functionality provided by the add-ons listed below.**
In Internet Explorer go to "Internet Options" screen, and select the "Programs" tab.
Click the Manage Add-ons button
Under Show: select All add-ons, disable these Microsoft add-ons
SharePoint OpenDocuments Class add-on
Office Document Cache handler add-on
Current status:
This is a known issue and is actively being looked at by the product groups right now. There is currently no estimated date for a fix to this issue. Check back to this blog entry, it will be updated once more information is available.