Jean-Francois:  
- Yes, a fractured joint is a Defect no matter which side of the board it is
on.  Yes, the fracture will most certainly over time penetrate to the other
side of the board.  Where connections are fractured/cracked the connection
should be reflowed.  You should also identify and eliminate the cause of the
fracture/crack.
- Defects (disturbed solder, poor wetting, insufficient solder coverage,
etc.) that are listed in IPC-A-610 should be considered Defects whether they
are present on the Top, Bottom, or Both sides of the board.
Regards, Jim Moffitt, Moffitt Consulting Service 317/773-5570