RKAttributeMapping lose custom value transformer when RKObjectMapping is inverted

In RKObjectMapping
On invertMapping:withPredicate:

Each mapping.attributeMappings is recreated with source/destination keyPaths inverted but its propertyValueClass and valueTransformer are not copied from original attributeMapping

Solution:
Implemented and used a new copyPropertiesFromMapping: method for RKAttributeMapping in the same way it already was for RKObjectMapping
Yes, you should be defining a custom transformer for each direction.