diff --git a/web/MinesweeperPanel.tsx b/web/MinesweeperPanel.tsx
index 88e35f3..799faa9 100644
--- a/web/MinesweeperPanel.tsx
+++ b/web/MinesweeperPanel.tsx
@@ -72,6 +72,9 @@ export const MinesweeperPanel = () => {
   const canvasRef = useRef<HTMLCanvasElement | null>(null);
   const rfbRef = useRef<RfbClient | null>(null);
   const buttonsRef = useRef(0);
+  // Every keysym we have sent a press for and not yet a release. A key held when focus leaves never gets
+  // its keyup, and a key stuck down on an X server stays stuck until something releases it.
+  const heldKeysRef = useRef(new Set<number>());
 
   const boxRef = useRef<HTMLDivElement | null>(null);
 
@@ -220,6 +223,7 @@ export const MinesweeperPanel = () => {
 
     rfbRef.current = rfb;
     return () => {
+      releaseHeldKeys();
       rfb.close();
       rfbRef.current = null;
       setConnected(false);
@@ -250,9 +254,28 @@ export const MinesweeperPanel = () => {
     const keysym = keysymFor(ev.key);
     if (keysym === null) return;
     ev.preventDefault();
+    if (down) heldKeysRef.current.add(keysym);
+    else heldKeysRef.current.delete(keysym);
     rfb.key(keysym, down);
   };
 
+  /**
+   * Release everything on the way out.
+   *
+   * A key held when the canvas loses focus never sends its keyup, and the server has no way to know: it
+   * stays down until something says otherwise. That is not a cosmetic leak — a stranded modifier turned
+   * every left click into a shift-click, which Minesweeper reads as a right click, and the board flagged
+   * instead of opening.
+   *
+   * Modifiers are no longer sent at all (see `keysymFor`), so this now covers the ordinary keys. Cheap,
+   * and the failure it prevents is invisible from the panel.
+   */
+  const releaseHeldKeys = () => {
+    const rfb = rfbRef.current;
+    for (const keysym of heldKeysRef.current) rfb?.key(keysym, false);
+    heldKeysRef.current.clear();
+  };
+
   const onPointer = (ev: React.MouseEvent<HTMLCanvasElement>, kind: 'down' | 'up' | 'move') => {
     const rfb = rfbRef.current;
     if (!rfb) return;
@@ -314,6 +337,7 @@ export const MinesweeperPanel = () => {
           onMouseMove={(ev) => onPointer(ev, 'move')}
           onKeyDown={(ev) => onKey(ev, true)}
           onKeyUp={(ev) => onKey(ev, false)}
+          onBlur={releaseHeldKeys}
           onContextMenu={(ev) => ev.preventDefault()}
           // Nearest-neighbour: smoothing a 1995 bitmap looks like a photograph of a screen rather than
           // the screen. It is half of what keeps this sharp; `stage` above is the other half.
diff --git a/web/rfb.ts b/web/rfb.ts
index 52bd01a..1814c91 100644
--- a/web/rfb.ts
+++ b/web/rfb.ts
@@ -380,13 +380,24 @@ const NAMED_KEYSYMS: Record<string, number> = {
   ArrowRight: 0xff53,
   ArrowDown: 0xff54,
   Insert: 0xff63,
-  Shift: 0xffe1,
-  Control: 0xffe3,
-  Alt: 0xffe9,
-  Meta: 0xffeb,
-  CapsLock: 0xffe5,
 };
 
+/*
+  MODIFIERS ARE DELIBERATELY ABSENT, AND THAT IS A FIX RATHER THAN AN OMISSION.
+
+  They were here, and it stranded `Shift_L` in the down state on the server: press shift, release it while
+  the canvas no longer has focus, and the keyup never arrives. Every left click then reached the game as
+  shift-click, which reads as a right click — the board flagged instead of opening and nothing about the
+  panel looked wrong.
+
+  They are not needed. `ev.key` is the character the layout ALREADY produced, so a shifted key arrives as
+  `A` and x11vnc presses shift itself to type it. Sending our own shift on top was redundant on the good
+  path and load-bearing on the bad one.
+
+  `keysymFor` returning null for them also means they stay the browser's, which is what you want: shift-tab
+  should still move focus out of a game of Minesweeper.
+*/
+
 export function keysymFor(key: string): number | null {
   const named = NAMED_KEYSYMS[key];
   if (named !== undefined) return named;