A particularly nasty bug is, reportedly, contained in some of the newest versions of Netscape and Internet Explorer for Windows. It affects the performance of the Java method copyArea, which is used to move chunks of pixels around within a drawable region. The Macintosh Runtime for Java has a related problem. Below is an applet that lets you check whether your particular browser is OK.
When you click "Go", the applet attempts to copy the middle red square, including the yellow border, the specified number of pixels to the right and down (negative values mean up and to the left). If the copyArea call works correctly, you will get an exact duplicate -- red square with yellow border. If not, you will probably get a messed-up square or parts of the outer black border will get transported along as well.
Try it with different values. If you see something obviously wrong, please
report it to the people responsible for your web browser. If they actually
listen to feedback and do something to correct the problem, then hopefully
Java will still have a future as a popular programming language.