I’ve noticed that with the 0.86 firmware, the ALC may cause problems with both black and white levels in some cases.
I noticed this when playing NHL 99 on a PAL PlayStation2, with an original Sony YPbPr cable. Along the top of the picture the black level increased somewhat to a dark gray, causing a gradient before it stabilized to a proper black level a few dozen lines down.
Reducing the ALC V filter from 1024 to 16 lines (with ALC H at 16 pixels and clamp/ALC offset left at 0) solved this. Adjusting the clamp/ALC offset did not help. I don’t know what upsets the ALC. Maybe there is graphics garbage in the back porch with NHL 99, but I’m not sure.
Even though it was possible to work around this problem in this case, I think it would be useful if there was a toggle to disable ALC altogether. Was it enabled in previous firmware versions?
In general you want to keep ALC enabled unless you prefer to set level manually each time for every source. Setting V filter to 16 should be safe and something I’ve considered making default in the next fw. There was once an option to disable it altogether but with the new filter options I’m not sure if such setting would be useful anymore.