I'm sure I'm not the only one puzzling over this, so I'd like to share a solution I came up with last night.
As of Jan 22, 2012, the latest version of the game has a glitch where you can't complete the 2nd set of bomb challenges. After playing for a while and crafting tons of bombs, I noticed I still didn't have two of the challenges:
- Craft a bomb with every shell type
- Craft a bomb of each effect type
Funny thing is, I did already have "Use every bomb effect at least twice". Apparently this glitch came up in the latest patch. It's affecting my copy on the Xbox, but it sounds like it's the same on PC and PS3. To complete this challenge and get the "Craft Maniac" achievement, delete the title update (but not your save files!). On the Xbox it's a single item, 9MB in size.
Then boot up the game again and select "cancel" when it prompts to download the title update. Note you'll have to move your saves out of cloud storage because you can't connect to live if you don't have the title update installed. After you complete the challenges and get the achievement, you can quit and download the update again.
I hope that helps somebody out.