FConfigCacheIni and int64

hello,

what is the ue4 syntax to be used with sprintf for an int64 ?

I am asking because I would like to add int64 support for ini files , like this

void FConfigCacheIni::SetInt64
(
const TCHAR*	Section,
const TCHAR*	Key,
int64				Value,
const FString&	Filename
)
{
    TCHAR Text[MAX_SPRINTF] = TEXT("");
    FCString::Sprintf(Text, TEXT("%i64d"), Value);
    SetString(Section, Key, Text, Filename);
}

bool FConfigCacheIni::GetInt64
(
const TCHAR*		Section,
const TCHAR*		Key,
int64&				Value,
const FString&	Filename
)
{
    FString Text;
    if (GetString(Section, Key, Text, Filename))
    {
        Value = FCString::Atoi64(*Text);
        return 1;
    }
    return 0;
}


but what I get when I read out the value is i.e.   
write  :  1000
read : 100064

so %i64d  is obviously not working. 

I noticed that SetDouble uses  %f  same as SetFloat  , is it the same for int64 ? Should I just use  %i  ? 

Some Clarification would be nice :)