Index: src/libchcore/TString.cpp
===================================================================
diff -u -N -r9479911a096555a7504c5c8a8eaee83ecb63440c -rbe86ea000c8ee746379fd5018c9f43a9b1cddfa1
--- src/libchcore/TString.cpp	(.../TString.cpp)	(revision 9479911a096555a7504c5c8a8eaee83ecb63440c)
+++ src/libchcore/TString.cpp	(.../TString.cpp)	(revision be86ea000c8ee746379fd5018c9f43a9b1cddfa1)
@@ -668,6 +668,8 @@
 	size_t stWhatLen = _tcslen(pszWhat);
 	size_t stWithWhatLen = _tcslen(pszWithWhat);
 
+	size_t stNewLen = stCurrentLength;
+
 	// resize internal string if needed
 	if(stWithWhatLen > stWhatLen)
 	{
@@ -681,14 +683,22 @@
 		}
 
 		if(stSizeDiff > 0)
-			EnsureWritable(stCurrentLength + stSizeDiff + 1);
+			stNewLen = stCurrentLength + stSizeDiff + 1;
 	}
 
+	bool bMadeWritable = false;
+
 	// replace
 	size_t stStartPos = 0;
 	size_t stFindPos = 0;
 	while((stFindPos = Find(pszWhat, stStartPos)) != std::numeric_limits<size_t>::max())
 	{
+		if(!bMadeWritable)
+		{
+			EnsureWritable(stNewLen);
+			bMadeWritable = true;
+		}
+
 		// Sample string "ABCdddb" (len:6), searching for "dd" (len 2) to replace with "x" (len 1)
 		// found string pos is: [stFindPos, stFindPos + stWhatLen)  -- sample ref: [3, 3 + 2)
 		// we need to
Index: src/libchcore/Tests/TestsTString.cpp
===================================================================
diff -u -N -r9479911a096555a7504c5c8a8eaee83ecb63440c -rbe86ea000c8ee746379fd5018c9f43a9b1cddfa1
--- src/libchcore/Tests/TestsTString.cpp	(.../TestsTString.cpp)	(revision 9479911a096555a7504c5c8a8eaee83ecb63440c)
+++ src/libchcore/Tests/TestsTString.cpp	(.../TestsTString.cpp)	(revision be86ea000c8ee746379fd5018c9f43a9b1cddfa1)
@@ -615,3 +615,13 @@
 	strValue.TrimRightSelf(L"gn");
 	EXPECT_EQ(strValue, L"Some stri");
 }
+
+TEST(TStringTests, ReplaceAffectingOtherStringInstancesBug)
+{
+	TString strValue(_T("Some string"));
+	TString strSecond(strValue);
+
+	strValue.Replace(_T("Some "), _T("No "));
+
+	EXPECT_EQ(strSecond, _T("Some string"));
+}