Lightroom Journal has posted the following warning: Potential JPEG Bug in Lightroom 3.4 and Camera Raw 6.4
The Lightroom and Camera Raw team would like to inform you of a potentially severe bug that was introduced in the Lightroom 3.4 and Camera Raw 6.4 update. 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. The team believes it’s very important to notify you of the risk and provide an estimate of when we will be able to deliver a correction in the form of Lightroom 3.4.1 and Camera Raw 6.4.1. We intend to have these updates available by Friday, May 27th.
If you do work with a significant number of JPEG files in Lightroom or Camera Raw and routinely update metadata (keywords, captions, etc) it would be prudent to wait for the updated release of Lightroom and Camera Raw.
The team would also like to thank Doug Cooper who reported this issue on the Lightroom Feedback Portal. Rare bugs like this make it quite difficult to pinpoint the source of the problem or even create a reproducible scenario but thanks to Doug’s persistence we were able to track down this bug quickly.
* To date we’ve only found one camera that generates these large blocks of private data, the HP PhotoSmart R607.