Well I remember reading about this a long time ago, how having two fans the same speed will do very little if anything.
Are you sure that you weren't reading something that confirms it doesn't just double the CFM? Because no it won't double the CFM just because you add to fans, but you WILL get an increase in airflow..that's a given...
It's common sense...to fans will produce more airflow than just one..
You can feel the increase air coming from the fans so it's not a debate whether you get an increase or not because you do...and it's not 'little to anything at all' either. It's not necessarily double CFM like I said though, but by the time the second fan starts to throw out the air it's already traveling quicker and much cooler.
I am mainly interested in how this happened in the first place.
Sorry lazer..can't say that any info you've given has lead to any specific causes.
Are you sure you didn't change something from Auto to User Define?
That would be the only way I could think of that option suddenly becoming available, but I've never heard of an option available for one try and then it just stops =/