FULL PRODUCT VERSION :
java version "1.6.0-rc"
Java(TM) SE Runtime Environment (build 1.6.0-rc-b104)
Java HotSpot(TM) Client VM (build 1.6.0-rc-b104, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows 2000 [Version 5.00.2195]

A DESCRIPTION OF THE PROBLEM :
Pattern.compile fails if the regex is either "\\\\Q\\\\E" or "\\\\E\\\\Q". I am trying to remove empty quoted/unquoted parts from a constructed regex. (The strings above translate to "\\Q\\E" and "\\E\\Q" respectively after Java String backslash expansion.)
If I insert a space between Q and E ("\\\\Q \\\\E") comile succeeds. Compile also succeeds if I use any other character (even regex special) in place of Q and E ("\\\\A\\\\B", "\\\\+\\\\*", etc.)

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
import java.util.regex.*;

public class Test {

   public static void main (String[] args) {
      Pattern p;
      // Fails
      p = Pattern.compile ("\\\\Q\\\\E");
      // OK
      p = Pattern.compile ("\\\\A\\\\B");
      // OK
      p = Pattern.compile ("\\\\+\\\\*");
   }
}

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The code above should execute without an exception.
ACTUAL -
Exception in thread "main" java.util.regex.PatternSyntaxException: Unexpected internal error near index 3
\\Q\\E
   ^
        at java.util.regex.Pattern.error(Unknown Source)
        at java.util.regex.Pattern.compile(Unknown Source)
        at java.util.regex.Pattern.<init>(Unknown Source)
        at java.util.regex.Pattern.compile(Unknown Source)
        at Test.main(Test.java:8)

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Exception in thread "main" java.util.regex.PatternSyntaxException: Unexpected internal error near index 3
\\Q\\E
   ^
        at java.util.regex.Pattern.error(Unknown Source)
        at java.util.regex.Pattern.compile(Unknown Source)
        at java.util.regex.Pattern.<init>(Unknown Source)
        at java.util.regex.Pattern.compile(Unknown Source)
        at Test.main(Test.java:8)

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.regex.*;

public class Test {

   public static void main (String[] args) {
      Pattern p;
      // Fails
      p = Pattern.compile ("\\\\Q\\\\E");
      // OK
      p = Pattern.compile ("\\\\A\\\\B");
      // OK
      p = Pattern.compile ("\\\\+\\\\*");
   }
}
---------- END SOURCE ----------