This has not always been around, in fact this bug is fairly recent. This bug occurred during tournaments and normal games. So the deal is, when you order a combine solider to throw a grenade they can refuse to do it but what makes it even worse is that they can get stuck in one position and not move for a few minutes shortly after they refuse to throw a grenade (sometimes forever). Its kinda funny, but awkward at the same time seeing your soliders all lined up in a line staring at a building not knowing how to throw a frag and cant be commanded :/
Really needs a fix
I will try to get some screenshots later =D