Was it before or was it after the last patch?
Today i have noted that the IS stay when you switching your weapon.
I was an SL and hold my rifle in IS, than i switch my weapon by press "2" to the pistol and i hold it in iron sight, directly.
I´m not sure it that is a "bug" or if that is wanted.
But i don´t like it very much. It makes the weapon switching very fast (and it feels very unrealistic)
When you are switching your weapon, you have to shoulder the first one (rifle) and than grab the second one (Pistol for example).
You need some time for this, and you will never be able to switch your weapon in 1,5 sec from rifle IS to pistol IS.
Tripwire, please change this.