Frankly, this code does not do what I would expect it to to do.

Maybe its just getting late, but I am not sure I see why this is odd. You are not duplicating the contents of the TYPEGLOB, but just aliasing it. It's just a level of indirection, not a copy of the package. In fact, just changing one line to this:

%Bar:: = %Foo::;
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Gives me this output

Expected class: Bar
Actual class: Bar
Expected class: Bar
Actual class: Bar
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Which is exactly what I would expect. And while I do agree the behavior you describe is not very clear, I am not sure I would have expected it to work without issue.