Last Lament

I'm playing Last Lament xbow and i know requiem interrupts if you get stunned/light stunned which is fine, i'm stunned so it's ok not to perform actions.

The issue here is that i'm using a stone charm (stun immunity), it does consume a charge when i get stunned and the xbow interrupts requiem even if i'm not stunned thanks to charm.

Where's the bug here, crossbow or charm?? I notice the stun hit on my character and the charm consuming 1 charge, at this point requiem stops and it switch to permafrost in 1 second delay.