When we compared behaviour of "set search_path" between 9.1.9 and 9.3.4, there is difference. On 9.1.9 the command "set search_path to schema1,public" checks if the schema exists and if not it return error. Example:
set search_path to "schema123",public;
ERROR: invalid value for parameter "search_path": "schema123, public"
DETAIL: schema "schema123" does not exist
On 9.3.4 the same command silently ignore the schema does not exists. Example:
set search_path to "schema123",public;
SET
select * from pg_namespace where nspname ilike '%schema123%';