This is something that's annoying me since updating to the latest ADT and SDK14.
I do have a lot of library projects and their references were converted from xxx_src folders to a 'Library Projects' folder during upgrade to the latest Android Development Environment. Everything works until the next Eclipse restart. These 'Library Projects' folders are gone after Eclipse restart - always.
So I have to right click all referencing projects one at a time --> Properties --> Android --> Remove the library project (it's still declared in there) --> Apply --> add the library project again --> Apply. Now the folder 'Library Projects' is back again - til the next Eclipse restart.
What's wrong here? Is there something that I can fix to make these 'Library Projects' folders stay permanent? Developing for Android is pure pain currently.