I opened kareha.pl, and it shows this.

kareha.pl
sub make_reply(%)
{

my (%vars)=@_;

my $thread=read_thread($vars{thread});

make_error(S_THREADCLOSED) if($$thread{closed});

$$thread{postcount}++;
$$thread{lastmod}=$vars{time};
$$thread{lasthit}=$vars{time} unless($vars{link}=~/sage/i or $$thread{postcount}>=MAX_RES or $$thread{permasage}); # bump unless sage, too many replies, or permasage

I also found this.
http://wakaba.c3.cx/docs/docs.html#KarehaConfig
MAX_RES (1000) - Maximum number of times a thread can be bumped

...I'm pretty sure that's not how muh japanese textboards work. I'm pretty sure people sage there mostly to delay bump limit. I can't really check because none of them let me fucking post on them.