Fix unregister cleanup

service.js

@@ -840,8 +840,8 @@ class BesService {
    * Creates auxiliary DOM elements for text adornments.
    */
   createCorrectionPanel() {
-    const panelParent = document.createElement('div')
+    this.panelParent = document.createElement('div')
-    panelParent.classList.add('bes-correction-panel-parent')
+    this.panelParent.classList.add('bes-correction-panel-parent')
 
     this.correctionPanel = document.createElement('div')
     this.correctionPanel.classList.add('bes-correction-panel')
@@ -851,9 +851,12 @@ class BesService {
     this.ctx = this.canvasPanel.getContext('2d')
     this.ctx.scale(1, 1)
 
-    panelParent.appendChild(this.correctionPanel)
+    this.panelParent.appendChild(this.correctionPanel)
     this.correctionPanel.appendChild(this.canvasPanel)
-    this.textElement.parentElement.insertBefore(panelParent, this.textElement)
+    this.textElement.parentElement.insertBefore(
+      this.panelParent,
+      this.textElement
+    )
     this.setCorrectionPanelSize()
   }
 
@@ -861,8 +864,7 @@ class BesService {
    * Clears auxiliary DOM elements for text adornments.
    */
   clearCorrectionPanel() {
-    this.correctionPanel.remove()
+    this.panelParent.remove()
-    this.canvasPanel.remove()
   }
 
   /**
@@ -2243,6 +2245,14 @@ class BesTAService extends BesPlainTextService {
     return service
   }
 
+  /**
+   * Unregisters grammar checking service.
+   */
+  unregister() {
+    super.unregister()
+    this.textElement.remove()
+  }
+
   /**
    * Creates a clone div element for the <textarea> element
    *