FULL PRODUCT VERSION :
java version "1.7.0_51"
Java(TM) SE Runtime Environment (build 1.7.0_51-b13)
Java HotSpot(TM) Client VM (build 24.51-b03, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 6.1.7601] (Windows 7, 32-bit)

A DESCRIPTION OF THE PROBLEM :
According to documentation (some parts omitted for brevity)

http://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html#compile%28java.lang.String,%20int%29

public static Pattern compile(String regex,
              int flags)
[...]

Throws:
    IllegalArgumentException - If bit values other than those corresponding to the defined match flags are set in flags

However, the class doesn't check the flag at all.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Just compile a Pattern with 0xFFFFFFFF (all bits set)

    Pattern.compile("d", 0xFFFFFFFF)

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
IllegalArgumentException, since not all 32 bits are used by the flags
ACTUAL -
No Exception thrown

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
/* Author: Hong Dai Thanh/nhahtdh */
import java.util.regex.*;

class BugCompileBadFlag {
    public static void main(String args[]) {
        try {
            System.out.println(Pattern.compile("d", 0xFFFFFFFF));
        } catch (IllegalArgumentException e) {
            System.out.println(e.getMessage());
        }
    }
}
---------- END SOURCE ----------