diff --git a/restoration/source410/BT_L4/GAUGE-BLOCK.NOTES.md b/restoration/source410/BT_L4/GAUGE-BLOCK.NOTES.md
index 6ffd0b04..af209788 100644
--- a/restoration/source410/BT_L4/GAUGE-BLOCK.NOTES.md
+++ b/restoration/source410/BT_L4/GAUGE-BLOCK.NOTES.md
@@ -1020,3 +1020,44 @@ correctly to 3/5/7).  Suspect the tile/strip blit for VertTwoPartBar-family
 widgets writing tile pixel VALUES rather than using them as a mask with the
 port colour -- the same widget draws correctly on the MFD heads, so it is
 specific to this port or this call site.
+
+--------------------------------------------------------------------------------
+5.3.41 -- the hunt for the plane-write defect: not caught, but bounded
+--------------------------------------------------------------------------------
+Two more hypotheses died, and the defect gained a nasty property.
+
+  5. PlayerStatus blitting `recoloredMech` through DrawPixelMap8 -- it is
+     dirty-gated (change-driven, matching the intermittency) and DOES blit an
+     8-bit pixmap.  KILLED: the widget map for a DIRTY run contains no
+     playerStatus at all.  It is built by cameraInit (the observer page) and
+     never exists in a mech cockpit.
+  6. Heat driving the coolant values and thus the change-driven redraw.
+     KILLED: a run with BT_FORCE_FIRE=1 (weapons firing, heat climbing) came
+     back clean.
+
+IT IS A HEISENBUG.  Rate across this session: dirty on roughly 3 runs in 25.
+Every run since instrumentation was added has been clean -- and the pattern
+lines up with STARTUP LOG VOLUME: runs with the attribute log or the blit
+trace enabled (hundreds of DEBUG_STREAM lines during init) are clean; the
+three dirty runs all had the lighter conf.  A chatty trace slows startup
+enough to suppress it, which is why the blit trace was narrowed to fire only
+for pixmaps landing on a NON-palette port (near-silent in the clean case).
+That narrowed trace did catch real traffic -- 17x17 PixelMap8 blits onto
+Mfd1/Mfd2/Mfd3, i.e. 8-bit pixmaps on single-bit planes -- but those render
+correctly (the MFD heads are within ~150px on clean runs), so the library
+evidently thresholds them.  Not the culprit, but the right bug class to keep
+watching.
+
+HUNTING RECIPE FOR NEXT TIME (two traps cost runs here):
+  * Detect dirty as Eng1 in (17981, 25000].  Eng1 == 0 means the cockpit is
+    not up yet, and my first detector read that as "dirty".
+  * Require the reading to be STABLE across two captures ~20s apart.  An
+    early capture during mission start caught a completely different frame --
+    a full 3-D cockpit view, purple sky, canopy struts, HUD reticle, with the
+    gauges at POD positions rather than plane-packed (Eng1 read 62927).  It
+    did not recur across 8 samples over the following minute, so it is an
+    early-run transient, not a persistent render.  Worth a look on its own
+    though: BTDPL.INI is in the mount and the engine's DPLRenderer is linked,
+    so the dPL path may be producing a frame during the launch sequence even
+    with L4VIDEO=OFF.  That is the first evidence this session that the 3-D
+    path emits anything at all -- do not confuse it with btl4vid being done.
diff --git a/restoration/source410/MUNGA/GRAPH2D.CPP b/restoration/source410/MUNGA/GRAPH2D.CPP
index 309033ed..07e586db 100644
--- a/restoration/source410/MUNGA/GRAPH2D.CPP
+++ b/restoration/source410/MUNGA/GRAPH2D.CPP
@@ -2588,6 +2588,43 @@ void
 
 		if (ClipImage(&sourceBounds, &position, pixelmap->Data.Size))
 		{
+			//
+			// BLIT TRACE (env BT_VIS_BLIT): every 8-bit pixmap that reaches
+			// a port, with the port it lands on and the rect it covers.
+			// Hunting the write that puts raw packed bytes into the
+			// plane-packed gauge buffer.
+			//
+			//
+			// Log ONLY pixmap blits landing on a port that is NOT one of the
+			// two palette ports (sec / overlay).  An 8-bit pixmap reaching a
+			// single-bit plane is the thing being hunted, and filtering here
+			// keeps the trace near-silent -- which matters, because the
+			// defect is a STARTUP TIMING race and a chatty trace suppresses
+			// it (six consecutive clean runs once logging was added).
+			//
+			if (getenv("BT_VIS_BLIT") != NULL
+			 && graphicsPort != NULL && graphicsPort->name != NULL
+			 && stricmp(graphicsPort->name, "sec") != 0
+			 && stricmp(graphicsPort->name, "overlay") != 0)
+			{
+				static int blitSamples = 0;
+				if (blitSamples < 400)
+				{
+					++blitSamples;
+					DEBUG_STREAM << "[blit] port='"
+						<< ((graphicsPort != NULL && graphicsPort->name != NULL)
+							? graphicsPort->name : "(null)")
+						<< "' at " << position.x << "," << position.y
+						<< " src " << sourceBounds.bottomLeft.x << ","
+						<< sourceBounds.bottomLeft.y << ".."
+						<< sourceBounds.topRight.x << ","
+						<< sourceBounds.topRight.y
+						<< " size " << pixelmap->Data.Size.x << "x"
+						<< pixelmap->Data.Size.y
+						<< " opaque=" << (opaque ? 1 : 0)
+						<< " rot=" << rotation << "\n" << flush;
+				}
+			}
 			graphicsPort->
 				DrawPixelMap8(
 					currentOperation,