1.3101 headers output after error on compilation error

I tried tracking down how or where the error is being output before the
headers, but couldn't track it down.
Mason::Exception's new returns $self, and at that point the error hasn't be
output yet.
Yet the only thing that happens after that is that Exception::Class dies on
the return.
 
I've been looking at a working Mason 1.27, Exception::Class 1.15 system, and
trying to work out how the headers get output first there, but can't see it.
Mason::Exception's new returns $self the same, and it just has the error
html in it, not the header, and Exception::Class dies at that point the
same.
 
Any idea what might be causing this or where I should look next?
 
Gareth Kirwan
Programming & Development,
Thermeon Europe Ltd,
[email protected]
Tel: +44 (0) 1293 864 303
Thermeon Europe e-Card: gbjk <http://www.thermeoneurope.com/e-Card/gbjk>