Not sure why it was such an issue with this one ride...
Because so much of the queue is open. It's much much easier to do it than, say, Peter Pan.

I'm still trying to figure out what TSMM is short for...
Toy Story Midway Mania.
It doesn't happen very often at WDW.
Oh, the people who post on long threads about the various ways and reasons to line-cut over on the Theme Parks board would likely disagree with you....
That part of the line where you can open the chain is both nice and not nice, depending on who is using it and why. If you get to that part and someone in your group has to use the bathroom like crazy, it's convenient. If people you don't know are using it for reasons you feel are wrong, it's not nice. I once was all twitchy about a big group of people that I felt were cutting b/c I didn't remember seeing them....then I saw them meet up with their group, and their group was HUGE (so half of their group was pretty big too) and then remembered that I did indeed see them all in line before...and then I felt really bad for thinking badly about them.
And I have a love hate relationship with that particular amount of chainlink... We got to that point and the line slowed way down, DS started messing with the chain which we don't allow but just as I said to stop it, he kind of fell, and hit his mouth hard on the links...cut the frenulum between top gums and upper lip, bled like crazy, hurt like crazy...I was GLAD that I could just unhook it and step out to clean it. DH stood right there, waiting, did NOT advance in line, just kept letting people in front of him. (which is the way to do it, in our opinion)
We got back, again through the helpful link, DS with a swollen upper lip...and we continued the ride.
And then we hate that section of chain b/c someone with a case of the nasties must have been touching/licking/whatevering the chain, b/c the next day DS started getting pretty sick, and when we got home he tested positive for strep. So we hate that chain! But DS certainly learned to not put his mouth on it after that! Even accidentally.
And my last thought about it all....if you're in line and someone has to "go", just talk to the CM!!! That happened with us once right in the thick of the Casey Jr line where you just can't get in or out easily unless you and those around you are very thin. We had DS hold it until we got up to the front of the line, and the CM pointed us to the exit, and then told us to come right back *to the exit*, and they would let us right in! We actually declined to do that, b/c the line was much shorter after the bathroom break, so we just got back in line, but it was super-nice for her to do that, and just goes to show taht if you do have a problem, the CMs are willing to help you!