It appears that Steel Trap was secretly changed a while back, and not many folks noticed. Though, perhaps more players had noticed, and I'm just behind the times, but I can at least take comfort that the ability wasn't updated on any major Simulations, either.
I most certainly didn't notice the change, though I could have sworn I checked when I last updated the Hunter Abilities page. Anyhow, I saw some of the hunters over at the SV Hunter Discord (which I've now decided is where I'll have to steal all of my blog topics from) talking about it; so I went to check my logs and sure enough.
The current version of Steel Trap lasts 33.3% longer (5 extra ticks) than the tooltip shows, doing 33.3% more damage overall, as each tick still does the same amount of damage.
I have no idea when this change might have happened, or even if it was intended or a bug. Regardless, it's a nice buff, making this a very good choice for single target damage, as it wasn't too far behind Caltrops or Guerrilla Tactics before. This also makes Steel Trap a solid option when a boss is being moved too much to get full up-time on Caltrops, Though Guerrilla Tactics will often do stronger DPS in that case if there are extra mobs up that you can hit with Explosive Trap.