.NET 5 RC2 WPF self-contained, single exe publish fails if its using assets from another .net 5 wpf project

When referring to a UserControl from another .net core 3.1 wpf project, the main project publish is successful.

When referring to a UserControl from another .net 5 wpf project, the main project publish fails, and outputs:

_Could not copy the file "..\singlefilehost.exe" because it was not found._

```
Main project csproj:

WinExe
net5.0-windows
true

Main project publish settings:

Release
Any CPU
bin\Release\net5.0-windows\publish\
FileSystem
net5.0-windows
win-x64
true
True
False
False
true

```