I'm a Java devloper. I have five different versions of the JDK and JRE installed, including 1.3.1. Why does the installer still insist that it isn't installed?

Pretty easy to check .. regedit,
HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment\1.3.1
.. exists!
String JavaHome = C:\Program Files\JavaSoft\JRE\1.3.1
.. exists!
C:\Program Files\JavaSoft\JRE\1.3.1\bin\hotspot\jvm.dll
.. exists!

How stupid is the installer?