Yes, this is truly for errors in the package itself. I'm good with warnings, just allowing someone to still run with scissors is the important part. ;-)
Actually now that I think about it, the experience should be the same for both scenarios for simplicity sake. If you have to reupload the same package due to errors, then it's the appending a date or increment to the end of the version and upload a new one.
In other words,
log4net.22.214.171.124.pkg has issues so re uploading is just the same concept as uploading a new version. you would change the version to 126.96.36.199.20100908 and then upload log4net.188.8.131.52.20100908 to the server.
The community would see this and know that it was a fix for a bad package. Then they can adjust accordingly. At least that is what I've been driving for on the nu project.
This kind of thing will usually only happen when people are not able to bump the version, ie. they are uploading someone else's package for them.