After discussion with Mystic and Rob, you now keep your lives, score and emerald count when changing maps in Co-op mode. Reset when you declare -force.

src/d_netcmd.c

@@ -1537,7 +1537,7 @@ void D_MapChange(INT32 mapnum, INT32 newgametype, boolean pultmode, boolean rese
 	CONS_Debug(DBG_GAMELOGIC, "Map change: mapnum=%d gametype=%d ultmode=%d resetplayers=%d delay=%d skipprecutscene=%d\n",
 	           mapnum, newgametype, pultmode, resetplayers, delay, skipprecutscene);
 
-	if (netgame || multiplayer)
+	if ((netgame || multiplayer) && !((gametype == newgametype) && (newgametype == GT_COOP)))
 		FLS = false;
 
 	if (delay != 2)
@@ -1703,9 +1703,19 @@ static void Command_Map_f(void)
 		}
 	}
 
+	// Prevent warping to locked levels
+	// ... unless you're in a dedicated server.  Yes, technically this means you can view any level by
+	// running a dedicated server and joining it yourself, but that's better than making dedicated server's
+	// lives hell.
+	if (!dedicated && M_MapLocked(newmapnum))
+	{
+		CONS_Alert(CONS_NOTICE, M_GetText("You need to unlock this level before you can warp to it!\n"));
+		return;
+	}
+
 	// don't use a gametype the map doesn't support
 	if (cv_debug || COM_CheckParm("-force") || cv_skipmapcheck.value)
-		; // The player wants us to trek on anyway.  Do so.
+		fromlevelselect = false; // The player wants us to trek on anyway.  Do so.
 	// G_TOLFlag handles both multiplayer gametype and ignores it for !multiplayer
 	// Alternatively, bail if the map header is completely missing anyway.
 	else if (!mapheaderinfo[newmapnum-1]
@@ -1724,19 +1734,10 @@ static void Command_Map_f(void)
 		CONS_Alert(CONS_WARNING, M_GetText("%s doesn't support %s mode!\n(Use -force to override)\n"), mapname, gametypestring);
 		return;
 	}
+	else
+		fromlevelselect = ((netgame || multiplayer) && ((gametype == newgametype) && (newgametype == GT_COOP)));
 
-	// Prevent warping to locked levels
+	D_MapChange(newmapnum, newgametype, false, newresetplayers, 0, false, fromlevelselect);
-	// ... unless you're in a dedicated server.  Yes, technically this means you can view any level by
-	// running a dedicated server and joining it yourself, but that's better than making dedicated server's
-	// lives hell.
-	if (!dedicated && M_MapLocked(newmapnum))
-	{
-		CONS_Alert(CONS_NOTICE, M_GetText("You need to unlock this level before you can warp to it!\n"));
-		return;
-	}
-
-	fromlevelselect = false;
-	D_MapChange(newmapnum, newgametype, false, newresetplayers, 0, false, false);
 }
 
 /** Receives a map command and changes the map.
@@ -1802,17 +1803,14 @@ static void Got_Mapcmd(UINT8 **cp, INT32 playernum)
 	if (demoplayback && !timingdemo)
 		precache = false;
 
-	if (resetplayer)
+	if (resetplayer && !FLS)
-	{
+		emeralds = 0;
-		if (!FLS || (netgame || multiplayer))
-			emeralds = 0;
-	}
 
 #ifdef HAVE_BLUA
 	LUAh_MapChange();
 #endif
 
-	G_InitNew(ultimatemode, mapname, resetplayer, skipprecutscene);
+	G_InitNew(ultimatemode, mapname, resetplayer, skipprecutscene, FLS);
 	if (demoplayback && !timingdemo)
 		precache = true;
 	CON_ToggleOff();

src/g_game.c

@@ -3541,7 +3541,7 @@ void G_DeferedInitNew(boolean pultmode, const char *mapname, INT32 pickedchar, b
 // This is the map command interpretation something like Command_Map_f
 //
 // called at: map cmd execution, doloadgame, doplaydemo
-void G_InitNew(UINT8 pultmode, const char *mapname, boolean resetplayer, boolean skipprecutscene)
+void G_InitNew(UINT8 pultmode, const char *mapname, boolean resetplayer, boolean skipprecutscene, boolean FLS)
 {
 	INT32 i;
 
@@ -3571,7 +3571,8 @@ void G_InitNew(UINT8 pultmode, const char *mapname, boolean resetplayer, boolean
 
 			if (netgame || multiplayer)
 			{
-				players[i].lives = cv_startinglives.value;
+				if (!FLS || (players[i].lives < cv_startinglives.value))
+					players[i].lives = cv_startinglives.value;
 				players[i].continues = 0;
 			}
 			else if (pultmode)
@@ -3585,13 +3586,16 @@ void G_InitNew(UINT8 pultmode, const char *mapname, boolean resetplayer, boolean
 				players[i].continues = 1;
 			}
 
+			if (!((netgame || multiplayer) && (FLS)))
+				players[i].score = 0;
+
 			// The latter two should clear by themselves, but just in case
 			players[i].pflags &= ~(PF_TAGIT|PF_TAGGED|PF_FULLSTASIS);
 
 			// Clear cheatcodes too, just in case.
 			players[i].pflags &= ~(PF_GODMODE|PF_NOCLIP|PF_INVIS);
 
-			players[i].score = players[i].xtralife = 0;
+			players[i].xtralife = 0;
 		}
 
 		// Reset unlockable triggers
@@ -5142,7 +5146,7 @@ void G_DoPlayDemo(char *defdemoname)
 	memset(playeringame,0,sizeof(playeringame));
 	playeringame[0] = true;
 	P_SetRandSeed(randseed);
-	G_InitNew(false, G_BuildMapName(gamemap), true, true);
+	G_InitNew(false, G_BuildMapName(gamemap), true, true, false);
 
 	// Set skin
 	SetPlayerSkin(0, skin);

src/g_game.h

@@ -89,7 +89,7 @@ void G_ChangePlayerReferences(mobj_t *oldmo, mobj_t *newmo);
 void G_DoReborn(INT32 playernum);
 void G_PlayerReborn(INT32 player);
 void G_InitNew(UINT8 pultmode, const char *mapname, boolean resetplayer,
-	boolean skipprecutscene);
+	boolean skipprecutscene, boolean FLS);
 char *G_BuildMapTitle(INT32 mapnum);
 
 // XMOD spawning