When using the older Silverlight portal, we can upload a deployment to staging, perform testing, make changes in VS, repackage, reupload to staging, rinse/repeat... without any sort of issue.
When we attempt to do the same with the newer HTML5 portal, it appears the browser is locking the deployment files on the local machine and preventing VS2010 from deleting them in order to package a new deployment. We have learned that by performing a full refresh in the browser (IE10 in this case), the files will become unlocked and we can successfully create a package. And yes, we are running Visual Studio as Administrator.
This is not the first time we noticed and reported this issue, but with the recent announcement that the Silverlight portal will be gone by end of summer we returned to the HTML5 portal and found the issue still exists.