First, I create a Shared add-in to customize the Backstage view of Word 2010. I have followed the steps in this MSDN page to create a shared add-in just for Word 2010: http://msdn.microsoft.com/en-us/library/ee691833.aspx. The shared add-in I created is BackStageCOMAddIn.zip
Second, I change the setting in Protected View to make the document opened from network show Protected view message bar. When I open a document from the internet, this document will load this ribbon. After clicking the Enable Editing, these two buttons in Backstage view disappear. For Protected view, I refer to this article: http://office.microsoft.com/en-us/excel-help/what-is-protected-view-HA010355931.aspx. Then, I upload a word document to http://skydrive.live.com, open it from internet, and now could see this Protected View message bar.
Third, for this behavior, then I create a VSTO word 2010 add-in, and an VSTO Excel 2010 add-in. By running this Word 2010 add-in, the behavior is the same as one in shared add-in. However, by running in Excel 2010 Add-in, these two buttons still show after clicking Enable Editing. The VSTO word Add-in I created is BackStageProtectedViewWordAddin.zip
It seems that this issue is only for Word 2010. So I think it may be a bug of Word 2010 32-bit.
The thread link is here: http://social.msdn.microsoft.com/Forums/en-US/worddev/thread/ecd3cc0f-90c5-4d40-9419-9341a9f5d88a.