Jackal Burst Adapter still prevents other rail slot items from being used, whereas it was supposed to work like the adaptive UBGL of the Punisher, i.e. that you can pick another rail attachment next to it.
From the patch notes (emphasis mine):
MG-S1 Jackal (TR SMG)
- BX Adapter no longer reduces magazine size, and uses the existing weapon ammo pool.
- BX Adapter now consumes two rounds per shot.
- BX Adapter's refire rate from 60ms to 80ms.
- BX Adapter no longer prevents rail slot items from being equipped.
It does, so fix it please, pretty please +.+
Edit: well I guess the servers are crashing left and right, so this is probably lower priority, but please don't forget about it for another 4 years!