fix(radio): deselect button if value doesn't match up with the group anymore

src/material/radio/radio.spec.ts

@@ -345,6 +345,27 @@ describe('MatRadio', () => {
       expect(radioInstances[2].checked).toBeFalsy('should not select the third button');
     });
 
+    it(`should update checked status if changed value to radio group's value`, () => {
+      groupInstance.value = 'apple';
+      radioInstances[0].value = 'apple';
+      fixture.detectChanges();
+
+      expect(groupInstance.selected).toBe(
+        radioInstances[0], 'expect group selected to be first button');
+      expect(radioInstances[0].checked).toBeTruthy('expect group select the first button');
+      expect(radioInstances[1].checked).toBeFalsy('should not select the second button');
+      expect(radioInstances[2].checked).toBeFalsy('should not select the third button');
+
+      radioInstances[0].value = 'watermelon';
+      fixture.detectChanges();
+
+      expect(groupInstance.value).toBeFalsy();
+      expect(groupInstance.selected).toBeFalsy('expect group selected to be null');
+      expect(radioInstances[0].checked).toBeFalsy('should not select the first button');
+      expect(radioInstances[1].checked).toBeFalsy('should not select the second button');
+      expect(radioInstances[2].checked).toBeFalsy('should not select the third button');
+    });
+
     it('should apply class based on color attribute', () => {
       expect(radioNativeElements.every(radioEl => radioEl.classList.contains('mat-accent')))
         .toBe(true, 'Expected every radio element to use the accent color by default.');

src/material/radio/radio.ts

@@ -402,14 +402,17 @@ export class MatRadioButton extends _MatRadioButtonMixinBase
   get value(): any { return this._value; }
   set value(value: any) {
     if (this._value !== value) {
+      const group = this.radioGroup;
       this._value = value;
-      if (this.radioGroup !== null) {
-        if (!this.checked) {
-          // Update checked when the value changed to match the radio group's value
-          this.checked = this.radioGroup.value === value;
-        }
+
+      if (group) {
+        // Update `checked`, because the button's value might not match up with the group anymore.
+        this.checked = group.value === value;
+
         if (this.checked) {
-          this.radioGroup.selected = this;
+          group.selected = this;
+        } else if (group.selected === this) {
+          group.selected = null;
         }
       }
     }