[facet.num.get.virtuals]/6 currently says:

Effects: If (str.flags()&ios_base::boolalpha) == 0 then input proceeds as it would for a long except that if a value is being stored into val, […]

It is unclear whether an implementation is allowed to call the overload for long in this case. Currently, libc++'s version calls that overload, while libstdc++ and MSVC STL's don't (example).

As the divergence implementation strategies is observable, perhaps we should clarify on this.