Why are the Beastmaster achievements not activating?

After playing through Act I, I have three entries missing in the "Beastmaster of Tristram" achievement:

• Butcher
• Dark Vessel
• Dark Berserker

I have the relevant lores in my bestiary (journal), but for some reason they won't activate the achievement when I read them.

I tried leaving the lores open and even clicking the "listen" button, but the checkbox in the achievement does not get filled.

I even started an Act I quest to read them there, no luck.

What am I doing wrong?

This is a bug related to the servers being overwhelmed for launch. Community Rep Bashiok says:

We're investigating lost/missing achievements. Nothing certain yet.

Many people are experiencing related issues. Blizzard is no doubt working first and foremost one ensuring the servers are up and that people can reliably connect, and then secondarily at other issues.

Update 1:

We're working on providing an update regarding issues with achievements. Please stay tuned. -Zarhym

Update 2:

We have communicated multiple times that we are aware of the Achievement issues and are still investigating. When we have more information to share, we will. Lack of updates does not mean we've forgotten about it. - Nethaera

Update 3: (5/17/12)

Not yet, we have a good handle on what's going on but we're still figuring out what action we can take. - Bashiok

Update 4: (5/24/12)

We also wanted to let you know that we're still looking into the best way to address the achievements that some players lost in the hours following the game’s release. While we don't have any concrete details to share with you just yet, we will have more information to share in the weeks ahead. We appreciate everyone's patience as we work to improve stability and usability for all players. - Nethaera

(Hopefully) Final Update: (6/12/12)

Blizzard just released Patch 1.0.2c, which says:

Achievements have been granted to players who previously completed their objectives, but were not correctly awarded completion credit.

Hopefully this will solve the issue!

I had a similar situation. Many of the achievements earned while the game was having networking problems/maintenance did not show up when I logged back on. Unfortunately, you can't earn the lore again once it's been recorded for that character - I tried. In order to get the lore again and earn the achievement, I had to playthrough with a second character and when the second character learned the lore/bestiary information, I got the achievements.