Potential JPEG Bug in Lightroom 3.4 and Camera Raw 6.4

Please note that this bug only impacts customers who are saving metadata to JPEG files with a rare characteristic.(JPEG files must have an unusually large block of private camera data included in the file to be susceptible to the bug*)   This scenario is so rare that we do not believe that it is necessary for customers who have already upgraded to revert to the previous version of Lightroom or Camera Raw.  However, the bug could cause image corruption which falls within our highest severity category of bugs.

Link: Potential JPEG Bug in Lightroom 3.4 and Camera Raw 6.4 « Lightroom Journal