When selecting from a table with a bytea field, the field is automatically filled with a single "x" character, meaning you have to clear it before an actual selection will work.
The problem is a result of the call to pg_escape_bytea in Postgres::escapeBytea (classes/database/Postgres.php). For some reason, when pg_escape_bytea("") is called in this function, it returns "\\x".
The confusing part is that if I write a script that does nothing but print the output of pg_escape_bytea(""), it returns an empty string as expected. I haven't figured out what phpPgAdmin does to alter the behaviour of this function.
I'm currently using phpPgAdmin 5.0.3-1, PostgreSQL 9.1+129ubuntu1, Apache 2.2.22-1ubuntu1, and php 5.3.10-1ubuntu3.4 under Ubuntu 12.04.1 LTS.