No function described in [input.output] except for
ios_base::imbue
and basic_filebuf::pubimbue
causes any instance of
basic_ios::imbue
or
basic_streambuf::imbue
to be called.
If any user function called from a function declared in [input.output] or
as an overriding virtual function of any class declared in [input.output]
calls
imbue,
the behavior is undefined.