Why do they cast it twice?

Hi, I've browsed the STL code a bit and stumble upon the next line (in
the operator << overload of both long and short outputs - the line is
for checking does the input is a manipulator)

long _Tmp = (_Bfl == ios_base::oct || _Bfl == ios_base::hex)
				? (long)(unsigned short)_Val //<-This Line
                                 : (long)_Val;

Is there any profound reason why they "Double" casting the _Val?
Thanks.