Console error when adding something inside the Custom HTML block, then saving and refreshing the page

[kmgalanakis]

If I add a custom HTML block inside the editor and type something inside it, when I save an reload the page, I get the following console error:

Warning: Failed prop type: You provided a `value` prop to a form field without an `onChange` handler. This will render a read-only field. If the field should be mutable use `defaultValue`. Otherwise, set either `onChange` or `readOnly`.
    in textarea (created by CodeEditor)
    in CodeEditor (created by LazyCodeEditor)
    in LazyCodeEditor
    in div
    in Unknown (created by State(WrappedComponent))
    in State(WrappedComponent) (created by BlockEdit)
    in BlockEdit (created by Align(BlockEdit))
    in Align(BlockEdit) (created by Anchor(Align(BlockEdit)))
    in Anchor(Align(BlockEdit)) (created by CustomClassName(Anchor(Align(BlockEdit))))
    in CustomClassName(Anchor(Align(BlockEdit))) (created by UseOnceValidation(CustomClassName(Anchor(Align(BlockEdit)))))
    in UseOnceValidation(CustomClassName(Anchor(Align(BlockEdit)))) (created by Dispatch(UseOnceValidation(CustomClassName(Anchor(Align(BlockEdit))))))
    in Dispatch(UseOnceValidation(CustomClassName(Anchor(Align(BlockEdit))))) (created by Select(Dispatch(UseOnceValidation(CustomClassName(Anchor(Align(BlockEdit)))))))
    in Select(Dispatch(UseOnceValidation(CustomClassName(Anchor(Align(BlockEdit)))))) (created by Filters(BlockEdit))
    in Filters(BlockEdit) (created by BlockListBlock)
    in BlockCrashBoundary (created by BlockListBlock)
    in div (created by IgnoreNestedEvents)
    in IgnoreNestedEvents (created by BlockListBlock)
    in div (created by IgnoreNestedEvents)
    in IgnoreNestedEvents (created by BlockListBlock)
    in BlockListBlock (created by ApiData(BlockListBlock))
    in ApiData(BlockListBlock) (created by Align(ApiData(BlockListBlock)))
    in Align(ApiData(BlockListBlock)) (created by Filters(ApiData(BlockListBlock)))
    in Filters(ApiData(BlockListBlock)) (created by WrappedComponent)
    in WrappedComponent (created by Connect(WrappedComponent))
    in Connect(WrappedComponent) (created by BlockListLayout)
    in div (created by BlockSelectionClearer)
    in BlockSelectionClearer (created by Connect(BlockSelectionClearer))
    in Connect(BlockSelectionClearer) (created by BlockListLayout)
    in BlockListLayout (created by Connect(BlockListLayout))
    in Connect(BlockListLayout) (created by Connect(Connect(BlockListLayout)))
    in Connect(Connect(BlockListLayout)) (created by BlockList)
    in BlockList (created by VisualEditor)
    in div (created by WritingFlow)
    in WritingFlow (created by Connect(WritingFlow))
    in Connect(WritingFlow) (created by VisualEditor)
    in div (created by BlockSelectionClearer)
    in BlockSelectionClearer (created by Connect(BlockSelectionClearer))
    in Connect(BlockSelectionClearer) (created by VisualEditor)
    in VisualEditor (created by WithViewportMatch(VisualEditor))
    in WithViewportMatch(VisualEditor) (created by Select(WithViewportMatch(VisualEditor)))
    in Select(WithViewportMatch(VisualEditor)) (created by Layout)
    in div (created by Layout)
    in div (created by Layout)
    in Layout (created by _class)
    in div (created by _class)
    in _class (created by Connect(_class))
    in Connect(_class)
    in Provider
    in ErrorBoundary
    in Provider (created by EditorProvider)
    in RichTextProvider (created by EditorProvider)
    in SlotFillProvider (created by EditorProvider)
    in APIProvider (created by EditorProvider)
    in DropZoneProvider (created by EditorProvider)
    in EditorProvider

[aduth]

Closing in favor of #5467