Marshall Levy at dvinfo.net posts an update on the firmware to fix the buffer problems with this camera. He says it should be available officially in 7-10 days. The firmware evidently fixes a problem in the camera - not the FMU - and takes about 3 minutes to install.
dvinfo.net: NX5U Firmware Update Particulars & Process
[UPDATE 5/27 7:15AM] Philip Johnston at HD Warrior says it's available now and provides a link to the Sony Europe support site BUT you need to register to access it, and you need a PC to carry out the Firmware update.
HD Warrior: Buffer Overflow problem in Sony NX5 Solved… Firmware V 2.00