This is how the ASP.NET Partial Trust does not guarantee application isolation KB article describes it:"...We previously described ASP.NET partial trust as a mechanism for enforcing application isolation in a shared hosting environment in which multiple applications that have different trust levels are hosted on the same web server. We are updating our guidance about this to reflect that running an ASP.NET page framework application in partial trust does not guarantee complete isolation from other applications that are running in the same process or on the same computer..."
I guess I could see this coming, since Partial Trust has been a massive failure with very little adoption and commercial use.
I wonder what prompted this announcement? I would bet that Microsoft found some nasty vulns in the PartialTrust environment which they can't (or won't) fix, so it's better to drop Partial Trust than to wait for a public disclosure.
It's actually quite sad to see such powerful idea and technology being dropped, but at least the good news is that it makes it more clear that running .NET code is a very dangerous activity and that we need better Sandboxing and SAST technologies.
I have always been a fan of .NET's partial trust, which was MUCH better designed and implemented than the Java Security Manager, and for a while it showed a path into a much safer .Net development environment.