given "-source 1.3" javac does not complain on Boolean.toString(boolean) as 1.4+

FULL PRODUCT VERSION :
java version "1.6.0_20"
Java(TM) SE Runtime Environment (build 1.6.0_20-b02)
Java HotSpot(TM) Server VM (build 16.3-b01, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
Linux lebuntu 2.6.32-24-generic #42-Ubuntu SMP Fri Aug 20 14:24:04 UTC 2010 i686 GNU/Linux

A DESCRIPTION OF THE PROBLEM :
Given "-source 1.3" javac does not complain on Boolean.toString(boolean) as 1.4+, while it should. Expected behavior is a failure to compile.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
compile a source containing Boolean.toString(false) using javac -source 1.3

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
failure to compile
ACTUAL -
compiles fine, no warnings, no errors.

REPRODUCIBILITY :
This bug can be reproduced always.