note 16563 rejected from function.call-user-func by jimw

I have more of a question than a comment. I am using the function call_user_func to call the function sprintf. Really, I'm using call_user_func_array, but same idea. I'm only using it because I want to be able to pass an array of arguments to sprintf instead of having to pass each argument to sprintf. (It makes my life easier in this case) Should this work?? It seems by the way the function is defined it should only call user functions, not system functions. sprintf seems like a system function to me. I'm not complaining because I like the way it is working for me, I'm just wondering if this is a feature that really is a bug that might get fixed in a future release and break my code. This is working on PHP 4.0.6 running on a Linux machine. Does any one have any thoughts or comments??