Explosive shotgun doesn't count as explosion for perks?

[Krileon]

I've been testing Rocket Launchers, Grenade Launchers, and Grenade Launcher Shotguns and only RL and GL are triggering the explosion perks. Is this a bug? Working as intended? Some clarification would be good as it makes sense for the GL Shotguns to count.

[Warlander]

I've been testing Rocket Launchers, Grenade Launchers, and Grenade Launcher Shotguns and only RL and GL are triggering the explosion perks. Is this a bug? Working as intended? Some clarification would be good as it makes sense for the GL Shotguns to count.

I would assume that the shotgun that fires grenades should count, if it doesnt write a bug report.