Well, doesn't it become a static target if it doesn't have to fall to score?
Also, lets not forget that if it doesn't properly fall, then the shooter has to determine...while the clock is running...if they need to reengage it, because of a miss... or not reengage it, because it did not fall. So, a faulty plate adds time (along with distraction) to a shooters attempt at the course of fire. It becomes "not the same for everybody"...thus, it probably should be a reshoot due to Range Equipment Failure.
I don't know that an inanimate object becomes anything, but anything sitting there not moving by definition would be static (popper, plate, paper, prop, etc) until acted upon by an outside force. Again, not sure that has anything to do with a nicked plate turning sideways and not falling. The plate turning sideways obviously is not static.
I don't think the argument that a shooter "determining" while the clock is running would be a reason to keep the rule as is either. This is Practical shooting. The premise of the sport is the shooter making decisions while shooting thorugh a scenario. Aren't distractions and judgment calls, which add time to the score, the reason for many stage designs?
If a plate is nicked and turns sideways without falling (obviously not set up per the rules) at a level I match, why not score it? I understand your reasoning, I just disagree with it.