diff --git a/docs/rh-log.txt b/docs/rh-log.txt
index 5b584a5a4..88c8a7c83 100644
--- a/docs/rh-log.txt
+++ b/docs/rh-log.txt
@@ -1,3 +1,23 @@
+February 24, 2007
+- Added << operators for FString that function exactly like +=, except they
+  are left-associative, so you can use them like you would with an ostream
+  and append to a string in a single expression without any overhead from
+  allocating temporary strings as would happen if you used the + operator.
+  In other words, instead of this:
+     string += "Some string " + "that is assembled" + " in parts";
+  You can do this and be more efficient while still being just as readable:
+     string << "Some string " << "that is assembled" << " in parts";
+- Changed PCD_PRINTBIND to include the command in its output if it isn't
+  bound.
+- Fixed: ACS_ExecuteWithResultValue could not be used inside a script because
+  DLevelScript::RunScript() was not reentrant, thanks to having a global stack.
+  The stack should be local to each instance of RunScript.
+- Fixed: rt_draw4cols() could get stuck in rare situations where it thinks it
+  should be drawing something but doesn't. Since long-term I plan to just
+  replace all the masked drawing the variants of maskwallscan, I'm not going
+  to try and find the real cause and fix it there. Instead, it just detects
+  the situation and bails out when it finds it.
+
 February 24, 2007 (Changes by Graf Zahl)
 - Fixed: In the Doom2 cast finale it was impossible to toggle the console.
 - Added APROP_Friendly actor property for ACS.
diff --git a/src/p_acs.cpp b/src/p_acs.cpp
index 63b911278..2bf1506fb 100644
--- a/src/p_acs.cpp
+++ b/src/p_acs.cpp
@@ -3,7 +3,7 @@
 ** General BEHAVIOR management and ACS execution environment
 **
 **---------------------------------------------------------------------------
-** Copyright 1998-2006 Randy Heit
+** Copyright 1998-2007 Randy Heit
 ** All rights reserved.
 **
 ** Redistribution and use in source and binary forms, with or without
@@ -102,8 +102,6 @@ struct CallReturn
 	int bDiscardResult;
 };
 
-static SDWORD Stack[STACK_SIZE];
-
 static DLevelScript *P_GetScriptGoing (AActor *who, line_t *where, int num, const ScriptPtr *code, FBehavior *module,
 	bool lineSide, int arg0, int arg1, int arg2, int always, bool delay);
 
@@ -2308,12 +2306,12 @@ int DLevelScript::RunScript ()
 		break;
 	}
 
-	int *pc = this->pc;
+	SDWORD Stack[STACK_SIZE];
 	int sp = 0;
+	int *pc = this->pc;
 	ACSFormat fmt = activeBehavior->GetFormat();
 	int runaway = 0;	// used to prevent infinite loops
 	int pcd;
-	//char workreal[4096], *const work = workreal+2, *workwhere = work;
 	FString work;
 	const char *lookup;
 	int optstart = -1;
@@ -3769,11 +3767,11 @@ int DLevelScript::RunScript ()
 				C_GetKeysForCommand ((char *)lookup, &key1, &key2);
 
 				if (key2)
-					work = work + KeyNames[key1] + " or " + KeyNames[key2];
+					work << KeyNames[key1] << " or " << KeyNames[key2];
 				else if (key1)
-					work += KeyNames[key1];
+					work << KeyNames[key1];
 				else
-					work += "???";
+					work << "??? (" << (char *)lookup << ')';
 			}
 			--sp;
 			break;
diff --git a/src/r_drawt.cpp b/src/r_drawt.cpp
index 89b9b967d..d63fcf831 100644
--- a/src/r_drawt.cpp
+++ b/src/r_drawt.cpp
@@ -861,6 +861,7 @@ void rt_draw4cols (int sx)
 		//			aBc
 		if (bad != 0 || maxtop > minbot)
 		{
+			int drawcount = 0;
 			for (x = 0; x < 4; ++x)
 			{
 				if (!(bad & 1))
@@ -869,15 +870,23 @@ void rt_draw4cols (int sx)
 					{
 						hcolfunc_post1 (x, sx+x, horizspan[x][0], horizspan[x][1]);
 						horizspan[x] += 2;
+						drawcount++;
 					}
 					else if (minnexttop > horizspan[x][0])
 					{
 						hcolfunc_post1 (x, sx+x, horizspan[x][0], minnexttop-1);
 						horizspan[x][0] = minnexttop;
+						drawcount++;
 					}
 				}
 				bad >>= 1;
 			}
+			// Drawcount *should* always be non-zero. The reality is that some situations
+			// can make this not true. Unfortunately, I'm not sure what those situations are.
+			if (drawcount == 0)
+			{
+				return;
+			}
 			continue;
 		}
 
diff --git a/src/zstring.h b/src/zstring.h
index ffb1f4ae3..ed51a73b5 100644
--- a/src/zstring.h
+++ b/src/zstring.h
@@ -121,6 +121,11 @@ public:
 	FString &operator += (const FName &name) { return *this += name.GetChars(); }
 	FString &AppendCStrPart (const char *tail, size_t tailLen);
 
+	FString &operator << (const FString &tail) { return *this += tail; }
+	FString &operator << (const char *tail) { return *this += tail; }
+	FString &operator << (char tail) { return *this += tail; }
+	FString &operator << (const FName &name) { return *this += name.GetChars(); }
+
 	FString Left (size_t numChars) const;
 	FString Right (size_t numChars) const;
 	FString Mid (size_t pos, size_t numChars) const;