diff --git a/OSBindings/Mac/Clock Signal.xcodeproj/xcshareddata/xcschemes/Clock Signal.xcscheme b/OSBindings/Mac/Clock Signal.xcodeproj/xcshareddata/xcschemes/Clock Signal.xcscheme
index 47f9c7286..1465a4f62 100644
--- a/OSBindings/Mac/Clock Signal.xcodeproj/xcshareddata/xcschemes/Clock Signal.xcscheme	
+++ b/OSBindings/Mac/Clock Signal.xcodeproj/xcshareddata/xcschemes/Clock Signal.xcscheme	
@@ -67,7 +67,7 @@
       </Testables>
    </TestAction>
    <LaunchAction
-      buildConfiguration = "Debug"
+      buildConfiguration = "Release"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       enableASanStackUseAfterReturn = "YES"
diff --git a/Storage/Disk/DiskImage/Formats/STX.cpp b/Storage/Disk/DiskImage/Formats/STX.cpp
index d2c6886cd..c53ce4ea0 100644
--- a/Storage/Disk/DiskImage/Formats/STX.cpp
+++ b/Storage/Disk/DiskImage/Formats/STX.cpp
@@ -56,9 +56,15 @@ class TrackConstructor {
 					std::vector<uint8_t> result;
 					result.reserve(size_t(end - begin) + prefix.size());
 
-					// Encode as MFM.
 					PCMSegment segment;
 					std::unique_ptr<Storage::Encodings::MFM::Encoder> encoder = Storage::Encodings::MFM::GetMFMEncoder(segment.data);
+
+					// Encode prefix.
+					for(auto c: prefix) {
+						encoder->add_byte(c);
+					}
+
+					// Encode body.
 					while(begin != end) {
 						encoder->add_byte(*begin);
 						++begin;
@@ -69,9 +75,6 @@ class TrackConstructor {
 					Shifter shifter;
 					shifter.set_should_obey_syncs(true);
 
-					// Add the prefix.
-					std::copy(prefix.begin(), prefix.end(), std::back_inserter(result));
-
 					// Add whatever comes from the track.
 					for(auto bit: segment.data) {
 						shifter.add_input_bit(int(bit));
@@ -243,6 +246,10 @@ std::shared_ptr<::Storage::Disk::Track> STX::get_track_at_position(::Storage::Di
 	const int track_index = (address.head * 0x80) + address.position.as_int();
 	if(!offset_by_track_[track_index]) return nullptr;
 
+	if(track_index == 41) {
+		printf("Y\n");
+	} else printf("N\n");
+
 	// Seek to the track (skipping the record size field).
 	file_.seek(offset_by_track_[track_index] + 4, SEEK_SET);