The code with extra debugging statements:

alias formats.do_highlight (type, win, ...)
{
	if (CONFIG.HIGHLIGHT && !match($1 $CONFIG.HIGHLIGHT_IGNORE_CHANNELS) &&
	    !match($0 $CONFIG.HIGHLIGHT_IGNORE_NICKS))
	{
		xdebug dword
		{
			xecho -b -c Inside xdebug dword;
			@ :have_match = match("*\\[$servernick() $CONFIG.HIGHLIGHT_LIST\\]*" $2-);
			xecho -b -c have_match: $have_match;
			if (match("*\\[$servernick() $CONFIG.HIGHLIGHT_LIST\\]*" $2-))
			{
				xecho -b -c PUBLIC "$*";
				formats.echo $type\_HL $*;
				if (CONFIG.HIGHLIGHT_BEEP)
				{
					^stack push set BEEP;
					^set BEEP ON;
					beep;
					^stack pop set BEEP;
				};
				if (CONFIG.HIGHLIGHT_NOTIFY && winvisible($win) < 1) {
					xecho -b -c Highlight triggered in window #$win by $0 \($1\);
				};

				return;
			};
		};
	};

	formats.echo $type $*;
};

Testing:
* Send a public from another client with "asdf"
* Send a public from another client with "client2_nick, test"

Results:

commit_id 2109

*** Inside xdebug dword
*** Inside xdebug dword
*** have_match: 0
<fudd> asdf
*** Inside xdebug dword
*** have_match: 1
*** PUBLIC "fudd #drunkards brian, test"
<fudd> brian, test

commit_id 2131

Inside xdebug dword
have_match: 1
PUBLIC "fudd #drunkards asdf"
Inside xdebug dword
have_match: 1
PUBLIC "fudd #drunkards brian, test"




###### TEST WITH /SET DEBUG 4

#### commit_id 2109

Function SERVERCTL(from_server) returned 0
Function SERVERCTL(get 0 nickname) returned brian
Function SERVERNICK() returned brian
Function WINCHAN(#drunkards) returned 1
Function MATCH(#drunkards ) returned 0
Function MATCH(fudd efudd) returned 0
*** Inside xdebug dword
Function SERVERCTL(from_server) returned 0
Function SERVERCTL(get 0 nickname) returned brian
Function SERVERNICK() returned brian
Function MATCH("*\[brian \]*" line 1) returned 0
*** have_match: 0
Function SERVERCTL(from_server) returned 0
Function SERVERCTL(get 0 nickname) returned brian
Function SERVERNICK() returned brian
Function MATCH("*\[brian \]*" line 1) returned 0
Function SPLIT(, PUBLIC) returned PUBLIC
Function CPARSE(<$1> $3-) returned <$1> $3-
Function FPARSE(PUBLIC fudd #drunkards line 1) returned <fudd> line 1
<fudd> line 1
Function SERVERCTL(from_server) returned 0
Function SERVERCTL(get 0 nickname) returned brian
Function SERVERNICK() returned brian


#### commit_id 2131

Function SERVERCTL(from_server) returned 0
Function SERVERCTL(get 0 nickname) returned brian
Function SERVERNICK() returned brian
Function WINCHAN(#drunkards) returned 1
Function MATCH(#drunkards ) returned 0
Function MATCH(fudd efudd) returned 0
Inside xdebug dword
Function SERVERCTL(from_server) returned 0
Function SERVERCTL(get  nickname) returned 
Function SERVERNICK() returned 
Function MATCH("*\[ \]*" line 1) returned 1
have_match: 1
Function SERVERCTL(from_server) returned 0
Function SERVERCTL(get  nickname) returned 
Function SERVERNICK() returned 
Function MATCH("*\[ \]*" line 1) returned 1
PUBLIC "fudd #drunkards line 1"
Function SPLIT(, PUBLIC_H) returned PUBLIC_H
Function SERVERCTL(from_server) returned 0
Function SERVERCTL(get 0 nickname) returned brian
Function SERVERNICK() returned brian