Topic Possible Bug - Achievement "Hold the Line"
I'm not certain on this one, and since I have the achievement now I can't reproduce it to test it, but I believe that if you build a new building in a place where a Nydus Worm spawns in the cinematic (thus removing your building), it counts as a loss as far as the achievement is concerned, despite the building staying up until the cinematic.
I'm not certain that this is the cause, but the building indeed does disappear during the cinematic (had extra bunkers built), and I hadn't (at least I'm fairly sure) lost any buildings prior to that.
I can confirm that this is not bugged, I just received the achievement by not building ANY buildings except for the barracks add-ons.
I'm well aware that you can get the achievement by not building. I did it myself. The problem I had is that buildings that don't get lost until the cinematic are causing the achievement to not be awarded, which is definitely a bug (got my brother to test it since he didn't have the achievement yet).
The same thing also happens in the first Terran challenge, by the way - if you put a unit into a medivac it counts as a loss for the purposes of calculating bronze/silver/gold.