ORMLite AutoIncrement doesn't work in PostgreSQL - ormlite-servicestack

Question

For some models in ORMLite I use Guid as Primary/Foreign Key - it allows to do bulk inserts without the need to do GetLastInsertedId() after each record inserted. I also use ShortId of int type for search purposes or passing in URL parameter (like blog post integer id) that should be autoincremented after each insert.
I don't understand how to make [AutoIncrement] work on non-primary key column in PostgreSQL.
What I'm doing wrong?
Here is an example of my class:
[Alias("ProductProperties")]
public class ProductProperty : IHasShortId, IHasName
{
public ProductProperty() { Id = Guid.NewGuid(); }
[PrimaryKey]
public Guid Id { get; set; }
[AutoIncrement]
public int ShortId { get; set; }
public string Name { get; set; }
[ForeignKey(typeof(ProductPropertyType))]
public int PropertyTypeId { get; set; }
}
It generates create table script with short_id as integer, not serial:
CREATE TABLE product_properties
(
id uuid NOT NULL,
short_id integer NOT NULL,
name text,
property_type_id integer NOT NULL,
CONSTRAINT product_properties_pkey PRIMARY KEY (id),
CONSTRAINT "FK_product_properties_product_property_types_PropertyTypeId" FOREIGN KEY (property_type_id)
REFERENCES product_property_types (short_id) MATCH Unknown
ON UPDATE NO ACTION ON DELETE NO ACTION
)
WITH (
OIDS=FALSE
);
ALTER TABLE product_properties
OWNER TO postgres;
UPDATE:
I was able to fix this by patching ORMLite source code:
https://github.com/ServiceStack/ServiceStack.OrmLite/blob/master/src/ServiceStack.OrmLite/OrmLiteConfigExtensions.cs#L127-L128
Commented the isPrimaryKey && line.
Also edited ServiceStack.OrmLite.OrmLiteDialectProviderBase.cs lines 385-403
from
if (isPrimaryKey)
{
sql.Append(" PRIMARY KEY");
if (autoIncrement)
{
sql.Append(" ").Append(AutoIncrementDefinition);
}
}
else
{
if (isNullable)
{
sql.Append(" NULL");
}
else
{
sql.Append(" NOT NULL");
}
}
to
if (autoIncrement)
{
sql.Append(" ").Append(AutoIncrementDefinition);
}
if (isPrimaryKey)
{
sql.Append(" PRIMARY KEY");
}
else
{
if (isNullable)
{
sql.Append(" NULL");
}
else
{
sql.Append(" NOT NULL");
}
}
Why does ORMLite restricts AutoIncrement to primary keys only?