Hi Michael,
i can fully confirm this for SD870 fw 1.00C with the latest Allbest 51 (trunk406) !
The ND filter setting in ExPhotOp has no effect at all, in scripts the set_nd_filter is also without effect (all tests done in manual mode).
I can always hear the ND filter swing in/out when moving the cam direct to a lamp, i can also see it (in the reflexions of the lenses) - but i can't control it, neither with the settings nor in a script.
Only in fireworks scene mode the ND filter is always out (not set) - also with direct light - and swings always in (is active) when half pressing the shutter.
I always get F8.0 when the ND filter is in (active) and F2.8 when it is out (inactive), in fireworks mode i always get F8.0.
The camera autonomous enables/disables the ND filter when moving into light (except the fireworks mode), regardless of any settings or script instructions, also while running the ND test script.