cursor cannot be displayed correctly in JTextPane

java version "1.3"
Classic VM (build JDK-1.3-F, green threads, sunwjit)

SunOS tuna 5.7 Generic sun4u sparc SUNW,Ultra-5_10

zh and zh.GBK

reproduce:
  compile and run the attached file.
  input something and press enter, and input something again,
  you will see the cursor is in wrong place