When a digital lockbox is dropped enough times, from a high enough distance, at some point the key compartment door is likely to pop open (if other damage does not occur to the lockbox first). This is no cause for alarm nor concern.
Digital lockboxes are designed to be secure when they are attached to a doorknob or similar fixture. They are at their most secure in this state. And they have been tested for security in this state.
We recommend against using digital lockboxes as untethered, free-standing key containers -- if for no other reason than the fact that someone could simply pick them up and walk off with them.