I found two bugs related to "Optimize library references"
When I open the dialog "optimize library references" and there are like three unused libraries, I select one, delete, then I select the second one and delete, it asks me every time that there was change in library tree, reload? There was only one change, when I previously removed the first unused reference. In this case there should not be such warning.
Second error, when I removed unused reference to System.Core in Windows Phone Silverlight project, and I added it again using the standard add refernece dialog, it was not added - the list of references was same after clicking OK to add System.Core. Why?