Broken: 2.78 2017-02-23
Short description of error
When setting the rigid body dynamics of an object so that "Enable Deactivation" and "Start Deactivated" are both enabled, the expected result is that the object is "activated on collision with other objects" (quote from the manual). Instead, the object is already activated when its bounding box and another active and dynamic rigid body object's bounding box intersect, even if the two objects never collide.
Exact steps for others to reproduce the error
Open the attached .blend, then start the animation (Alt-A or click on play) and watch closely at what point the capital T is activated (it starts falling down).
Alternatively, there are two small spheres behind the text. The top sphere is deactivated, but the bottom one immediately activates it even though they don't collide.