I've had the same problem as well with NHibernate (On .NET) with Postgres ENUM types. Luckily, NHibernate is incredibly powerful and you *can* get everything working flawlessly, however it takes some serious digging into the source code and reading the docs to figure it out. The main issue is that NHibernate, out of the box, wants to map an ENUM as a number. For example:
INSERT INTO FOO SomeEnumColumn VALUES (1);
This will cause an error, because PG is looking for a string value (Even though ENUMs are stored as numeric values under the covers). It's pretty easy to configure NHibernate to convert ENUMs to strings (there's tons of blog posts on that).. However, this causes NHibernate to write:
INSERT INTO FOO SomeEnumColumn VALUES ('EnumValue'::text);
Which will also cause an error. I've found the only way around it is to configure NHibernate to treat ENUMs as "Objects" which will simply generate:
INSERT INTO FOO SomeEnumColumn VALUES ('EnumValue'); -- No casting here, yay!
This works. However, to agree with the original poster's point, if Postgres could be a little more forgiving about values that could be interpreted as correct (like an implicit cast between numeric and enum and string and enum) then we wouldn't have these issues..
Mike