The molotov-smoke bug fixed in the patch notes of 9/26/2017 has not been completely solved, as demonstrated by the Reddit user Lil_wortel7.
The bug causes the smoke to not go off when hitting a molotov’s fire. Instead, it bounces as if hitting standard terrain. It can be easily explained by how a molotov works.
How a molotov spreads the fire
Once a molotov hits the ground, the fire spreads randomly. The fire consists of multiple “mini-fires”, so it just spawns many of these around the first contact point.
All mini-fires have their own hitbox, but there are some gaps in between them. They are too small for players to notice, and damage can’t be avoided standing on one of them, but a smoke grenade is small enough to hit one of these empty spaces.
Valve announced that the bug was fixed in the patch notes of 9/26/2017:
Fixed rare cases when smoke would not extinguish fire when it bounces between the flames.
The Reddit user Lil_wortel7 shared a video demonstrating that the bug is still in the game.
Valve indeed fixed many cases in which the bug occurred, but these kind of problems are very hard to deal with. Every time a specific case is reproducible, their team must code a way to solve it.
In the end, you shouldn’t worry about it as the bug will very rarely affect your games.
Header image by Harry Ahokas