Hi,

We have a page (StartPage) which has a block property (FeatureBlock), which in turn contains another block property (ImageBlock). Editing any property inside FeatureBlock using on-page editing on StartPage results in a serialization-error. The payload (propertyName=feature&propertyValue={"imageBlock":{"image":"21681","altText":"Alt tekst"},"title":"Title","ingress":"","buttonText":"","buttonUrl":null}&id=6_25091&renderSettings={"BackgroundClass":"feature-box-block--with-bg"}) seems well formed when posted to /EPiServer/CMS/PropertyRender/Render, but the property value for the ImageBlock ends up as a string which cannot be deserialized. The issue is not present when editing in all properties view. I'm also not sure when this issue first occured.

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EPiServer.Core.InvalidPropertyValueException: "{
  "image": "21681",
"altText": "Alt text"
}" is not a valid value for "Image".
---> System.InvalidCastException: Unable to cast object of type 'System.String' to type 'xxx.ImageBlock'.
   at EPiServer.SpecializedProperties.PropertyBlock`1.<>c__DisplayClass12_0.<set_Value>b__0()
   at EPiServer.Core.PropertyData.SetPropertyValue(Object value, SetPropertyValueDelegate doSet)
   --- End of inner exception stack trace ---
   at EPiServer.Core.PropertyData.ThrowEditorFriendlyException(Object value, Exception e)
   at EPiServer.Core.PropertyData.SetPropertyValue(Object value, SetPropertyValueDelegate doSet)
   at EPiServer.SpecializedProperties.PropertyBlock`1.set_Value(Object value)
   at EPiServer.Cms.Shell.Json.Internal.BlockDataConverter.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.DeserializeConvertable(JsonConverter converter, JsonReader reader, Type objectType, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonSerializer.Deserialize(TextReader reader, Type objectType)
   at EPiServer.Framework.Serialization.Json.Internal.JsonObjectSerializer.Deserialize(TextReader reader, Type objectType)
   at EPiServer.Shell.Serialization.Json.Internal.CompositeJsonObjectSerializer.Deserialize(TextReader reader, Type type)
   at EPiServer.Cms.Shell.UI.Controllers.Internal.PropertyRenderController.DeserializeValue(String value, Type propertyType)
   at EPiServer.Cms.Shell.UI.Controllers.Internal.PropertyRenderController.Render(String propertyName, String propertyValue, String id, String renderSettings, String epslanguage)
   at lambda_method1085(Closure, Object, Object[])
   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.SyncActionResultExecutor.Execute(ActionContext actionContext, IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Logged|12_1(ControllerActionInvoker invoker)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
 at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync()

I realize the issue could likely be worked around by using ContentReference properties instead of using the actual block itself, but this is a big project with many editors already used to the existing workflow, and many existing properties would lose existing data with such a change.