This unfortunately a bit complicated example shows a problem related to inheriting a variadic template from another variadic template. The base class has a virtual method with the parameter pack as parameter, implemented in the subclass. In addition, the subclass has a member of a template type which is initiated from ctor parameters which are a variant of the parameter pack. When the base has been initiated the "variantness" of the types is "forgotten" by the compiler when initiating the member. Or something like that.
In my real code, before boiling it down maximally to show this issue in the attached file I get a subsequent internal compiler error:
1> Generating Code...
1>c:\ru\proplist.hpp(413): fatal error C1001: An internal error has occurred in the compiler.
1> (compiler file 'f:\dd\vctools\compiler\utc\src\p2\main.c', line 211)