InstanceLockOut

1.2

• Added command to manually apply a reset.

1.1

• Updated interface versions.

1.0

• See InstanceLockOut's web-page for more information.

So there are a few unavoidable problems with the addon. Lets put it this way, Blizzard certainly don't make it easy to keep good track of instance resets and such; there are many triggers for instance resetting that are undetectable. For example, at its current state it is impossible to tell if your party leader resets instances. There used to be more system messages, but they seemed to have dissapeared over the patches.
Currently if you're party leader or playing solo InstanceLockOut will work most flawlessly. Only current problem that I could fix is when the party changes/disbands that can also cause instance resets. I'll try work out a method for this but currently I just don't know how it truely works.