I had the same thing happen to me. I got the achievement for 100 kills, but none for 20 kills. It's not a huge deal for me though since its only worth like 5 points. but still kinda annoying. 

This exact thing happened to me last night.  I got thru the 3rd stage already.  I think I will probably restart it tonight since it won't take that long to replay through those pieces.  This game looks like a relatively easy S rank although I'm betting hard is pretty brutal given that some of the stuff on normal is already stupid challenging.  But I also think its partly because I haven't gotten a total grip on the combo system/what moves work on what guys yet.  Really enjoying this game so far though

Weird.

i normally do that with all trials i play

thanks for the heads up. buying that game tomorrow.

I watched a friend play this over ustream earlier and immediately swore it off. After watching his narrowly survive an encounter by tossing a pair of enemies away then filling them full of his remaining bullets THEN jumping a huge dude and juggling him with a chainsaw... well, I think you see where I'm going with this. :)

This happened to me. I didn't delete my savegame, though, I'm still working on getting all the costumes. I think I'll just wait for the fix.
 
EDIT: Crap. It also stops you getting the 'The Wrong Guy' achievement. That's 15g off.

The developer acknowledges that 8/12 of the achievements are broken.  That's why I haven't bought this yet.