Steps to reproduce:
-setup remote CRAN repo, add to virtual repo
-resolve a package
-wait a day, then check https://cran.r-project.org/web/packages/available_packages_by_date.html for an updated package. Try to install the updated package version
-see that the new version is not available, even with a Metadata retrieval cache period of 0 for the virtual repository. However, if you try to resolve from the remote repo, it will work. Then, the virtual repo metadata will merge and update, so the new version will be available.
Resolving from the virtual first to get a new package should trigger the remote to update its metadata and merge the new metadata.