i did a try with this thing in 2.2rc3.
but the problem still remains.

Doing a lot of code-searching and hacking i found that the save-button
call's admin/?executeForm=EditForm.ReferencedField.DetailForm&fieldName=MyListName
It was difficult for me, as a rookie, to find the corresponding 'function' part in Silverstripe.
turned out that soemhow there the follwong function is called:

ComplexTableField
..
function saveComplexTableField() {
}

if i do a die at the start of this function the save-button
end's his 'active state', but of course nothing is saved.
problem is doing Debug::message
doesn't show me anything (becouse here we are in a popup window, i think)
this makes things hared to find out.
maybe there's some possibility to do a trace (log) within silverstripe?

and maybe this can help someone else who has the same problem ;-)
i'll keep you informed...

UPDATE:
Found the documentation for having logging / tracing in files: COOL
http://doc.silverstripe.com/doku.php?id=error-handling
i added
ini_set("log_errors", "On");
ini_set("error_log", "php_error.html");
to my _config.php
and used fe..
error_log('BEFORE childObject-write');
within code
but there's no file php_error.html in the saphire directory (neither in cms..)
would be cool to get any hint...

btw.
$childObject->write();
makes the troubles,
a die before the command, and buttons stops working
only a die after, and the button hangs...