Well I guess it gets confused because of the extra s at the end of Types of Packagings name.
CakePHP uses inflection to determine singular from plural names.
The name of the table could be improved in that fact that you use packaging_types instead of types_of_packaging
If you still want to keep that old name try to remove the s at the end of types_of_packagings
Because for me the singluar should be Type of packaging and the plural Types of packaging
But PackagingType and PackagingTypes is a bit more clearer I would say 