FULL PRODUCT VERSION :
java version "1.6.0_19"
Java(TM) SE Runtime Environment (build 1.6.0_19-b04)
Java HotSpot(TM) Client VM (build 16.2-b04, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
We have two files in "test" directory.

======DIR=======
C:\test>dir
 Volume in drive C has no label.
 Volume Serial Number is 941B-42F4

 Directory of C:\test

05/21/2010 02:47 PM <DIR> .
05/21/2010 02:47 PM <DIR> ..
05/21/2010 02:44 PM 0 a_file
05/21/2010 02:44 PM 0 not_a_file.
               2 File(s) 0 bytes
               2 Dir(s) 17,429,995,520 bytes free
======DIR=======

Following code shows that java determines "a_file" as a file, but "not_a_file." as not a file.
The reason is that file "not_a_file." has '.' (dot) as the latest symbol.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
File a_file isFile() = true
File not_a_file. isFile() = true
ACTUAL -
File a_file isFile() = true
File not_a_file. isFile() = false

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
package test;

import java.io.File;
import java.io.IOException;

public class FileIsNotAFileTest {
    public static void main(String[] args) throws IOException {
        File dir = new File("./test");
        for (File file : dir.listFiles()) {
            System.out.print("File "+file.getName());
            System.out.println(" isFile() = "+file.isFile());
        }
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Use !isDirectory() to test if file is really file