Jon "Flightblogger" Ostrower reported that the prime reason for the production halt was not just for suppliers to catch up with production work but also to allow Boeing and it's suppliers to fix a design flaw. The flaw can potentially compromise the structural integrity of the airplane. Flightblogger reported that the flaw was discovered in December, 5 months ago.
The flaw involves shear ties which attaches the fuselage skin to the fuselage structure in section 48 and 48 aft. When there are repeated changes in the thermal condition of the rear fuselage, the shear ties can detach from the aircraft skin thus creating the structural issue.
Flightblogger reports that the situation does not represent an immediate safety of flight issue to the test flight fleet and that a fix is identified. The fix involves using thicker shear ties and radius filler alongside the existing shear ties. Boeing says that all airplanes will meet FAA requirements.
LN 23 and LN 24 are being modified now at Charleston with some modification work to be done at Everett. LN 25 will have the fix installed partly in Charleston and partly in Korea where the section 48 Aft is manufactured. The existing airplanes will be modified though apparently ZA001, ZA002 and ZA003 will not receive them as they will not be sold to customers. All customer airplanes are going to receive the modifications. Thus airplanes from LN 4 to LN 22 will all have to receive the modifications and starting with LN 55 the 787 will have a permanent fix in the section 48. Now while there has been some supplier issues that have lead to the temporary halt in production, Flightblogger's sources has said that the shear tie issue is the main reason for the halt. I will try to get more details about this issue.
Boeing said that the issue will not effect first delivery or continued production of the 787.
Flightblogger: Source: 787 design flaw drives supplier freeze