I don't know if this is well known or not - but it took me by surprise. We
all know the JDBC incompatibilities between JDK1.3 and JDK1.4, but my
understanding was the except this, it is ok to compile with JDK1.4 and
have the code run under JDK1.3.

Not true. I had axis1.0 compiled with JDK1.4 ( I assume more recent code
will have the same problem ), and it failed on JDK1.3 with "no such
method". The code used StringBuffer.append( StringBuffer ). In JDK1.4,
this is a new method and the code compiled to use the new method. If you
compile with JDK1.3 - the compiler will call the append( Object ) method,
which does a String.valueOf().

The conclusion - compile releases with JDK1.3.