That is correct. I used the UPS migrator to create the schema i believe. I have one installation and i've always seen this issue. I don't think its a modelling problem as the vast majority of device registrations go without error.

Seems Ok to me:

CREATE TABLE category
(
id bigint NOT NULL,
name character varying(255),
CONSTRAINT category_pkey PRIMARY KEY (id)
)

CREATE TABLE installation
(
id character varying(255) NOT NULL,
alias character varying(255),
device_token character varying(4096),
device_type character varying(255),
enabled boolean NOT NULL,
operating_system character varying(255),
os_version character varying(255),
platform character varying(255),
variant_id character varying(255),
CONSTRAINT installation_pkey PRIMARY KEY (id),
CONSTRAINT fk_q1c2n4kjui158w3t1llg99koq FOREIGN KEY (variant_id)
REFERENCES variant (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
)

CREATE TABLE installation_category
(
installation_id character varying(255) NOT NULL,
category_id bigint NOT NULL,
CONSTRAINT installation_category_pkey PRIMARY KEY (installation_id, category_id),
CONSTRAINT fk_dttushnsf13kdwywyba8njqv7 FOREIGN KEY (installation_id)
REFERENCES installation (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT fk_ox56uwmry1x6kfoi3dkw1to8o FOREIGN KEY (category_id)
REFERENCES category (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
)