I got latent black cleft for normal monster

You mean a normal monster dropped it? That's perfectly normal, no bug.

Latent sunders can drop from normal monsters now. Heralds, however, have a much higher chance of dropping them. The Herald that spawned later has nothing to do with the drop.

When RoTW first came out (back in February), latent sunders would drop only from Heralds.

In patch 3.2 (came out May 19th), they changed it so sunders can drop from any monster or chest that can drop a Gheed's Fortune (a consequence being that Gheed's Fortune became harder to find). Before 3.2 your unique grand charm from a normal mob would have been guaranteed a Gheed's Fortune, now it’s a random roll between Gheed's Fortune and a latent sunder.

In patch 3.3 (released 3 days ago), the situation is still the same, they only tweaked the relative rarity of Gheed's Fortune vs sunders so whenever any non- Herald drops a unique grand charm it may still be a sunder but more likely to be a Gheed's Fortune than in patch 3.2.

I have had 3 Latent charms (2 cold and 1 crack of heavens) drop from regular mobs. First Cold one was last week and about 2 hours later another Cold. Wasn't until yesterday did the third drop. After the last Cold drop, I did get one drop from a Herald before I got Crack of Heavens drop.

If you're not actively hunting heralds you'll probably have a thousand normal monster kills for every Herald kill. So if you get a latent sunder drop it is much more likely coming from a normal monster than from a Herald.