Notswap was updated to also include swapping weapon ammo types.
For example primary -> primary or special->special in the same slot is fine but you cant go primary->special or special -> primary without it being drained.
[quote]Expanded the Not Swap modifier to cover changing ammo types in either your Kinetic or Energy slot mid-life.[/quote]
https://www.bungie.net/7/en/News/article/destiny_2_update_7_3_6