diff --git a/js/CustomShapeMenu.js b/js/CustomShapeMenu.js
index a1a0be0..2bde6a1 100644
--- a/js/CustomShapeMenu.js
+++ b/js/CustomShapeMenu.js
@@ -88,6 +88,8 @@ export class CustomShapeMenu {
         `;
         // Add main auto-apply checkbox to the new container
         const checkboxContainer = this._createCheckbox(() => `${this.canvas.autoApplyShapeMask ? "☑" : "☐"} Auto-apply shape mask`, () => {
+            // Always hide any active shape preview lines first to prevent them from getting stuck
+            this.canvas.maskTool.hideShapePreview();
             this.canvas.autoApplyShapeMask = !this.canvas.autoApplyShapeMask;
             if (this.canvas.autoApplyShapeMask) {
                 this.canvas.maskTool.applyShapeMask();
@@ -108,6 +110,7 @@ export class CustomShapeMenu {
             this.canvas.shapeMaskExpansion = !this.canvas.shapeMaskExpansion;
             this._updateUI();
             if (this.canvas.autoApplyShapeMask) {
+                this.canvas.maskTool.hideShapePreview();
                 this.canvas.maskTool.applyShapeMask();
                 this.canvas.render();
             }
@@ -201,6 +204,7 @@ export class CustomShapeMenu {
             this.canvas.shapeMaskFeather = !this.canvas.shapeMaskFeather;
             this._updateUI();
             if (this.canvas.autoApplyShapeMask) {
+                this.canvas.maskTool.hideShapePreview();
                 this.canvas.maskTool.applyShapeMask();
                 this.canvas.render();
             }
diff --git a/js/MaskTool.js b/js/MaskTool.js
index ca53eee..b4e67e2 100644
--- a/js/MaskTool.js
+++ b/js/MaskTool.js
@@ -1005,11 +1005,18 @@ export class MaskTool {
      * Hide shape preview and switch back to normal mode
      */
     hideShapePreview() {
+        // Cancel any pending throttled preview updates to prevent race conditions
+        if (this.shapePreviewThrottleTimeout !== null) {
+            clearTimeout(this.shapePreviewThrottleTimeout);
+            this.shapePreviewThrottleTimeout = null;
+        }
+        // Clear any pending preview parameters
+        this.pendingPreviewParams = null;
         this.isPreviewMode = false;
         this.shapePreviewVisible = false;
         this.clearShapePreview();
         this.shapePreviewCanvas.style.display = 'none';
-        log.debug("Shape preview hidden");
+        log.debug("Shape preview hidden and all pending operations cancelled");
     }
     /**
      * Clear shape preview canvas
diff --git a/src/CustomShapeMenu.ts b/src/CustomShapeMenu.ts
index 5b44fab..4a65893 100644
--- a/src/CustomShapeMenu.ts
+++ b/src/CustomShapeMenu.ts
@@ -113,6 +113,9 @@ export class CustomShapeMenu {
         const checkboxContainer = this._createCheckbox(
             () => `${this.canvas.autoApplyShapeMask ? "☑" : "☐"} Auto-apply shape mask`,
             () => {
+                // Always hide any active shape preview lines first to prevent them from getting stuck
+                this.canvas.maskTool.hideShapePreview();
+                
                 this.canvas.autoApplyShapeMask = !this.canvas.autoApplyShapeMask;
                 
                 if (this.canvas.autoApplyShapeMask) {
@@ -140,6 +143,7 @@ export class CustomShapeMenu {
                 this._updateUI();
                 
                 if (this.canvas.autoApplyShapeMask) {
+                    this.canvas.maskTool.hideShapePreview();
                     this.canvas.maskTool.applyShapeMask();
                     this.canvas.render();
                 }
@@ -252,6 +256,7 @@ export class CustomShapeMenu {
                 this._updateUI();
                 
                 if (this.canvas.autoApplyShapeMask) {
+                    this.canvas.maskTool.hideShapePreview();
                     this.canvas.maskTool.applyShapeMask();
                     this.canvas.render();
                 }
diff --git a/src/MaskTool.ts b/src/MaskTool.ts
index 0dd8ac4..015d6d7 100644
--- a/src/MaskTool.ts
+++ b/src/MaskTool.ts
@@ -1265,11 +1265,20 @@ export class MaskTool {
      * Hide shape preview and switch back to normal mode
      */
     hideShapePreview(): void {
+        // Cancel any pending throttled preview updates to prevent race conditions
+        if (this.shapePreviewThrottleTimeout !== null) {
+            clearTimeout(this.shapePreviewThrottleTimeout);
+            this.shapePreviewThrottleTimeout = null;
+        }
+        
+        // Clear any pending preview parameters
+        this.pendingPreviewParams = null;
+        
         this.isPreviewMode = false;
         this.shapePreviewVisible = false;
         this.clearShapePreview();
         this.shapePreviewCanvas.style.display = 'none';
-        log.debug("Shape preview hidden");
+        log.debug("Shape preview hidden and all pending operations cancelled");
     }
 
     /**