To clarify matters for all those concerned about this issue, I have just spoken to our engineers and they assure me that these two aircraft are undergoing some scheduled ground inspections to support the well publicised procedures of keeping residual fuel in the centre tanks on most Boeings. The aircraft will be back in service as soon as these are completed. No individual issues surround these two aircraft.
I trust that this explains the issue to those who would seek to make something out of nothing!