Creating an instance of a class that derives from Ext.data.Model requires both 'Ext.data.reader.Json' and 'Ext.data.writer.Json' by default (as they are the default reader and writer) but these are not required by Ext.data.Model.
Steps to reproduce the problem:
Create an instance of a class that inherits from Ext.data.Model without first loading the JSON reader or writer classes
The result that was expected:
The reader and writer classes are in the list of dependencies for Ext.data.Model
The result that occurs instead:
The reader and writer classes are not in the list of dependencies and Ext.Loader attempts to synchronously load them. This doesn't work when synchronous loading is disabled.
The following just creates a grid property model (just as a class that inherits from Ext.data.Model). Nothing to see except the warning messages in the console.