Tapestry 4.1 and jdk issues

I am developing a couple of components for Tapestry 4.1. They are meant to go into the final release of Tapestry Bayeux 2.0.0.
But I am having some difficulties getting a clear answer whether or not Tapestry 4.1 is java 1.4 compatible.
Just up until now I thought it was because tapestry 4.0 was and haven't seen any notes saying different about the 4.1 release. But now I am in doubt because I am having trouble executing on of my a testcases compiled by java 1.4.
I keep getting:

java.lang.UnsupportedClassVersionError:
org/apache/tapestry/markup/MarkupFilter (Unsupported major.minor version 49.0)

The error indicate that tapestry 4.1 has been compiled using java 5 and I am trying to compile and execute my test using java 1.4.

To further strengthen my theory I stumbled across the following code in the tap 4.1 source which uses autoboxing, hence can only be compiled by java 5.

org.apache.tapestry.dojo.form.Autocompleter
from line 268:
/**
* {@inheritDoc}
*/
public boolean isAsync()
{
return Boolean.TRUE;
}

If I have to compile using tapestry 4.1, is it correct that my only solution is to go with java 5 and no longer support java 1.4 runtimes?

I did some google searching: site:tapestry.apache.org/tapestry4.1 jdk but I only managed to find the following phrase on the page describing the upgrade from 3.0 to 4.0.
"Part of the transition to Tapestry 4.0, and targetting (in a later release) a minimum JDK of 1.5,..."
A later release seems to be Tapestry 4.1!

I miss a clear statement telling what java version tapestry is compiled by and what runtimes tapestry 4.1 supports.

You are more than welcome to enlighten me if you know the answer.