[fpc-pascal] overloading function

[LacaK]

Hi,
I am trying understand how FPC determines which version of overloaded 
function to call.
Take as example these 2 functions (from SysUtils):
1. function StrPLCopy(Dest: PChar; Source: string; MaxLen: SizeUInt): 
PChar; overload;
2. function StrPLCopy(Dest: PWideChar; const Source: UnicodeString; 
MaxLen: SizeInt): PWideChar; overload;

And in program I use:
var p: pointer;
      s: string;
begin
   StrPLCopy(p, s, 10);
end;

It seems, that 2nd "unicode" version of StrPLCopy is called. But why?
I am thinking as:
1st parameter is untyped pointer, so no one of function can be prefered
2nd parameter is "string" which exactly match 1st function signature
3rd parameter is "integer constant" which mach both signatures

So it seems to me, that 1st version of function signature matches 
better, because of exact match of 2nd parameter ... why is then called 
2nd version?
-Laco.