It is a very good question. Hope someone who has access to the code will tell us the difference.
I confirm the UDF works perfectly:
create function dbo.test
returns datetime
as
begin
declare @res datetime
select @res=convert(char(12), current_date()) + convert(char(8), current_time())
return @res
end
go
select dbo.test()
go
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Aug 28 2013 3:02PM