A postgres session (or postgresql.conf file) accepts the parameter 'debug_print_plan' [1]: if set to 'on' (or 1) postgresql will write planner details to the logfile:

$ psql
psql (9.3devel)
Type "help" for help.

testdb=# set debug_print_plan=1;
SET
testdb=# select 42;
 ?column?
----------
       42
(1 row)

testdb=# \q


2012-10-30 23:57:03.757 CET 21837 LOG:  plan:
2012-10-30 23:57:03.757 CET 21837 DETAIL:     {PLANNEDSTMT
           :commandType 1
           :queryId 0
           :hasReturning false
           :hasModifyingCTE false
           :canSetTag true
           :transientPlan false
           :planTree
              {RESULT
              :startup_cost 0.00
              :total_cost 0.01
              :plan_rows 1
              :plan_width 0
              :targetlist (
                 {TARGETENTRY
                 :expr
                    {CONST
                    :consttype 23
                    :consttypmod -1
                    :constcollid 0
                    :constlen 4
                    :constbyval true
                    :constisnull false
                    :location 7
                    :constvalue 4 [ 42 0 0 0 0 0 0 0 ]
                    }
                 :resno 1
                 :resname ?column?
                 :ressortgroupref 0
                 :resorigtbl 0
                 :resorigcol 0
                 :resjunk false
                 }
              )
              :qual <>
              :lefttree <>
              :righttree <>
              :initPlan <>
              :extParam (b)
              :allParam (b)
              :resconstantqual <>
              }
           :rtable <>
           :resultRelations <>
           :utilityStmt <>
           :subplans <>
           :rewindPlanIDs (b)
           :rowMarks <>
           :relationOids <>
           :invalItems <>
           :nParamExec 0
           }

2012-10-30 23:57:03.757 CET 21837 STATEMENT:  select 42;
[download]

This is all written to the logfile so to me it seems not very likely the case for the OP. He (or some SQL-generator) probably just forgot to take an 'EXPLAIN'-prefix from an SQL statement.

[1] runtime-config-logging.html (postgres manual)

update (2012.10.30): show use in session setting (not postgresql.conf setting).