Apache2::Filter internal flush error

Hello mod_perl-ers,

I'm seeing a fair amount of these in my apache error log:

Apache2::Filter internal flush: (-3) Unknown error 4294967293 at -e line 0

I'm running apache 2.2.29, mod_perl 2.0.8 on linux.

Looking at the source code, it looks like I'm getting into this else-block
in 'src/modules/perl/modperl_error.h':

 if (rc != APR_SUCCESS) {
            if (APR_STATUS_IS_ECONNRESET(rc) ||
                APR_STATUS_IS_ECONNABORTED(rc)) {
                ap_log_error(APLOG_MARK, APLOG_INFO, 0, s,
                             "%s got: %s", func,
                             modperl_error_strerror(aTHX_ rc));
            }
            else {
                modperl_croak(aTHX_ rc, func);
            }
        }


What cases fall into the else-block?  What is the best way to debug?

Thanks,

Paul