Questions within Custom Components do not display survey variable val…

…ues fix #7640

src/question_custom.ts

@@ -660,7 +660,8 @@ export class QuestionCustomModel extends QuestionCustomModelBase {
     return this.contentQuestion;
   }
   protected getDefaultTitle(): string {
-    if(this.hasJSONTitle && this.contentQuestion) return this.contentQuestion.title;
+    if(this.hasJSONTitle && this.contentQuestion)
+      return this.getProcessedText(this.contentQuestion.title);
     return super.getDefaultTitle();
   }
   setValue(name: string, newValue: any, locNotification: any, allowNotifyValueChanged?: boolean): any {

tests/question_customtests.ts

@@ -2658,3 +2658,25 @@ QUnit.test("showPreview & default value, #7508", function (assert) {
   assert.equal(contentQuestion.value, "edf", "contentQuestion.value #4");
   ComponentCollection.Instance.clear();
 });
+QUnit.test("showPreview & default value, #7640", function (assert) {
+  ComponentCollection.Instance.add({
+    name: "customtext",
+    questionJSON: {
+      type: "text",
+      title: "abc={abc}"
+    },
+  });
+
+  const survey = new SurveyModel({
+    elements: [
+      { type: "customtext", name: "q1" }
+    ]
+  });
+  const q1 = <QuestionCustomModel>survey.getQuestionByName("q1");
+  const contentQuestion = <QuestionTextModel>q1.contentQuestion;
+  survey.setVariable("abc", 123);
+  assert.equal(contentQuestion.locTitle.renderedHtml, "abc=123", "contentQuestion.title");
+  assert.equal(q1.locTitle.renderedHtml, "abc=123", "q1.title");
+
+  ComponentCollection.Instance.clear();
+});