I'm seeing something similar - the focal length is available, but the lens name isn't. Raw files are native .dng format from my Pentax K10d, and all the metadata, including the missing lens name, is visible in the Pentax supplied Raw viewer. Selecting an image, or a group of images in folder view in LR, then running the 'Update previews and metadata' command restores the lens type metadata, but is very slow for a large number of files. Is this is a bug, or some kind of problem with the Pentax .dng files (.crw files from my Canon 10D that LR has converted to .dng don't show this problem) or am I just missing something?
Any help or comments would be appreciated!
Cheers
Steve Morton