Update:
When lowering the distance to subject, the number jumps sometimes. For example, when decreasing and reaching 0, 88 appears, then 0 again. Or when increasing it, 10 11 12 102 12 13 etc. These are frequent numbers, but not the only ones with the problem.
Also, sometimes when decreasing the value, it instantly jumps to zero from whatever number I am at the moment.
Anyway, the manual distance is disabled when I press the ALT button. If I press it again, it's shown again as enabled. So apparently it would only work in script mode. I haven't tried any script yet, so I really don't know.
Regards