diff --git a/keen.c b/keen.c
index ddb8b64..ec6e512 100644
--- a/keen.c
+++ b/keen.c
@@ -1784,6 +1784,20 @@ static char *interpret_move(const game_state *state, game_ui *ui,
         if (ui->hpencil && state->grid[ui->hy*w+ui->hx])
             return NULL;
 
+        /*
+         * If you ask to fill a square with what it already contains,
+         * or blank it when it's already empty, that has no effect...
+         */
+        if ((!ui->hpencil || n == 0) && state->grid[ui->hy*w+ui->hx] == n &&
+            state->pencil[ui->hy*w+ui->hx] == 0) {
+            /* ... expect to remove the cursor in mouse mode. */
+            if (!ui->hcursor) {
+                ui->hshow = false;
+                return UI_UPDATE;
+            }
+            return NULL;
+        }
+
 	sprintf(buf, "%c%d,%d,%d",
 		(char)(ui->hpencil && n > 0 ? 'P' : 'R'), ui->hx, ui->hy, n);
 
diff --git a/solo.c b/solo.c
index f6c7172..addcf80 100644
--- a/solo.c
+++ b/solo.c
@@ -4704,6 +4704,26 @@ static char *interpret_move(const game_state *state, game_ui *ui,
         if (ui->hpencil && state->grid[ui->hy*cr+ui->hx])
             return NULL;
 
+        /*
+         * If you ask to fill a square with what it already contains,
+         * or blank it when it's already empty, that has no effect...
+         */
+        if ((!ui->hpencil || n == 0) && state->grid[ui->hy*cr+ui->hx] == n) {
+            bool anypencil = false;
+            int i;
+            for (i = 0; i < cr; i++)
+                anypencil = anypencil ||
+                    state->pencil[(ui->hy*cr+ui->hx) * cr + i];
+            if (!anypencil) {
+                /* ... expect to remove the cursor in mouse mode. */
+                if (!ui->hcursor) {
+                    ui->hshow = false;
+                    return UI_UPDATE;
+                }
+                return NULL;
+            }
+        }
+
 	sprintf(buf, "%c%d,%d,%d",
 		(char)(ui->hpencil && n > 0 ? 'P' : 'R'), ui->hx, ui->hy, n);
 
diff --git a/towers.c b/towers.c
index 57d6614..e0dad48 100644
--- a/towers.c
+++ b/towers.c
@@ -1483,6 +1483,20 @@ static char *interpret_move(const game_state *state, game_ui *ui,
         if (state->clues->immutable[ui->hy*w+ui->hx])
             return NULL;
 
+        /*
+         * If you ask to fill a square with what it already contains,
+         * or blank it when it's already empty, that has no effect...
+         */
+        if ((!ui->hpencil || n == 0) && state->grid[ui->hy*w+ui->hx] == n &&
+            state->pencil[ui->hy*w+ui->hx] == 0) {
+            /* ... expect to remove the cursor in mouse mode. */
+            if (!ui->hcursor) {
+                ui->hshow = false;
+                return UI_UPDATE;
+            }
+            return NULL;
+        }
+
 	sprintf(buf, "%c%d,%d,%d",
 		(char)(ui->hpencil && n > 0 ? 'P' : 'R'), ui->hx, ui->hy, n);
 
diff --git a/undead.c b/undead.c
index 46ecce3..70a5f4c 100644
--- a/undead.c
+++ b/undead.c
@@ -1769,22 +1769,30 @@ static char *interpret_move(const game_state *state, game_ui *ui,
         if (xi >= 0 && !state->common->fixed[xi]) {
             if (button == 'g' || button == 'G' || button == '1') {
                 if (!ui->hcursor) ui->hshow = false;
+                if (state->guess[xi] == 1)
+                    return ui->hcursor ? NULL : UI_UPDATE;
                 sprintf(buf,"G%d",xi);
                 return dupstr(buf);
             }
             if (button == 'v' || button == 'V' || button == '2') {
                 if (!ui->hcursor) ui->hshow = false;
+                if (state->guess[xi] == 2)
+                    return ui->hcursor ? NULL : UI_UPDATE;
                 sprintf(buf,"V%d",xi);
                 return dupstr(buf);
             }
             if (button == 'z' || button == 'Z' || button == '3') {
                 if (!ui->hcursor) ui->hshow = false;
+                if (state->guess[xi] == 4)
+                    return ui->hcursor ? NULL : UI_UPDATE;
                 sprintf(buf,"Z%d",xi);
                 return dupstr(buf);
             }
             if (button == 'e' || button == 'E' || button == CURSOR_SELECT2 ||
                 button == '0' || button == '\b' ) {
                 if (!ui->hcursor) ui->hshow = false;
+                if (state->guess[xi] == 7 && state->pencils[xi] == 0)
+                    return ui->hcursor ? NULL : UI_UPDATE;
                 sprintf(buf,"E%d",xi);
                 return dupstr(buf);
             }
@@ -1841,11 +1849,13 @@ static char *interpret_move(const game_state *state, game_ui *ui,
             }
             if (button == 'e' || button == 'E' || button == CURSOR_SELECT2 ||
                 button == '0' || button == '\b') {
-                sprintf(buf,"E%d",xi);
                 if (!ui->hcursor) {
                     ui->hpencil = false;
                     ui->hshow = false;
                 }
+                if (state->pencils[xi] == 0)
+                    return ui->hcursor ? NULL : UI_UPDATE;
+                sprintf(buf,"E%d",xi);
                 return dupstr(buf);
             }
         }       
diff --git a/unequal.c b/unequal.c
index 5e9994f..c1d3a30 100644
--- a/unequal.c
+++ b/unequal.c
@@ -1612,6 +1612,25 @@ static char *interpret_move(const game_state *state, game_ui *ui,
         if (ui->hpencil && GRID(state, nums, ui->hx, ui->hy) > 0)
             return NULL;        /* can't change hints on filled square (!) */
 
+        /*
+         * If you ask to fill a square with what it already contains,
+         * or blank it when it's already empty, that has no effect...
+         */
+        if ((!ui->hpencil || n == 0) &&
+            GRID(state, nums, ui->hx, ui->hy) == n) {
+            bool anypencil = false;
+            int i;
+            for (i = 0; i < state->order; i++)
+                anypencil = anypencil || HINT(state, ui->hx, ui->hy, i);
+            if (!anypencil) {
+                /* ... expect to remove the cursor in mouse mode. */
+                if (!ui->hcursor) {
+                    ui->hshow = false;
+                    return UI_UPDATE;
+                }
+                return NULL;
+            }
+        }
 
         sprintf(buf, "%c%d,%d,%d",
                 (char)(ui->hpencil && n > 0 ? 'P' : 'R'), ui->hx, ui->hy, n);