I've now released version 2.1.1 Beta of Armadillo Run, which fixes most of the simulation-related bugs found in 2.1.0.
The biggest problem was with the collision response, which I inadvertently made more unpredictable/random in 2.1.0. I think this is largely fixed now, and is more like the version 1 behaviour (but without the dark force).
The 'explosion' bugs in 2.1.0 that were caused by many links being placed on top of each other should be reduced, but there will still be some force created by using this technique. I decided this was better than disallowing all overlapping links in the editor.
I've also fixed the invisible armadillo bug.
The version 2.1.1 Beta release is available to everyone who's already bought the game from your download/registration link in your purchase confirmation email. If you don't have this any more, you can also get to your download/registration page by entering your current registration code here:
http://www.armadillorun.com/buy/registration.php