Be careful if you use Bullet's "deflector" group because all those particles will use the Floor node's "Shape" setting.
SC handles this properly and deflector particles use their SC voxel settings.
This has been reported to Cebas and hopefully they can find a solution.
In the meantime, be sure to either:
1) use ONLY the BT group setting and include the proper tree for collisions
2) set BT's Floor "Shape" parameter to a shape that will work for what you want (probably as Mesh)
The help file discusses this, so be sure to read things carefully.