Entries are getting overwritten in the Native OData offline cache.
According to the OData specification, the Entry ID should be a universally unique identifier. The cache design is based on this principle. If the Entry IDs are not unique, change the OData provider design to generate unique Entry IDs as indicated by the Open Data Protocol specifications. For more information about the specifications, see: http://msdn.microsoft.com/en-us/library/ff478141.aspx#edn6 .
The Entry IDs must be in the form of an IRI (International Resource Identifier), which is an international version of the URI (Uniform Resource Identifier), like a URL (Uniform Resource Locator), you see in the address bar of your browser. The URI does not have to reference a resource on the network.