When "Immovable" is on, it seems to disable(set to 0) all properties of the object - Elasticity, Friction, etc.
When "Movable" is on, the equation seems to combine both the elasticity of Object1 and Object2 to calculate the bounce, amongst others.
The Manual says only Density is set to 0 with Immovable on.
Thus you should be able to manually choose elasticity for an Immovable object, no? One wall should be bouncier than the other, for example.
Immovable completely disabling all physics properties does seem to cancel that possibility.
This makes having, for example, different types of surfaces on the same Layout quite difficult, no?