I just posted a blog entry on an issue with Ligthroom 2.5, Camera Raw 5.5 and DNG Converter 5.5 that affects Mac PowerPC customers. Please read the entry here: http://blogs.adobe.com/lightroomjournal/2009/09/important_note_regarding_light.html
Unfortunately, the comments on the Lightroom Journal blog do not seem to be functioning so please comment in this thread.
Lightroom, Camera Raw, DNG Product Manager
There was a request for further clarity on how to revert to Camera Raw 5.4. Please follow these instructions:
1. Close Photoshop CS4 and Bridge CS4
2. Download the Camera Raw 5.4 plug-in from the following location: http://www.adobe.com/support/downloads/detail.jsp?ftpID=4521
3. Navigate to: (Please read directory carefully)
Library/Application Support/Adobe/Plug-Ins/CS4/File Formats
4. Delete the Camera Raw.plug-in file located in that directory
5. Open the Camera_Raw_5_4 DMG file downloaded in step 2
6. Copy the Camera Raw.plug-file from the DMG file into the direcotry indicated in step 3.
I discovered the same artifact when using DNG files from the Leica M8 with the new ACR 5.5 and Lightroom 2.5. Reverting back to ACR 5.3 and Lightroom 2.3 eliminated the problem!! An Adobe fix is anxiously awaited..............Sposner2