Given the number of issues reported with metadata conflicts in Lightroom, I watch the "Metadata Status" panel religiously as I make changes.
What I see in LR 3.4.1 is that if I add or delete a keyword in about a dozen images (raw images with sidecars), metadata status is incorrectly reported as < mixed > even after all the changes have been actually written to the files. I know that it has been written because (a) if I deselect and reselect the images in LR, then the metadata is correctly reported as "up to date", and (b) I can see by monitoring the date modified in Finder that in fact the metadata is being updated. It is just not being reported correctly in LR.
Sometimes when I add or remove a keyword (clicking on checkbox in Keyword List panel) for a selected group of photos I will see the metadata status flash to "< mixed >", then "up to date", then, after a pause, flip back to "< mixed >".
It appears that this bug is related to a timing issue, as the bug appears when I select around a dozen images. It does not occur with less than 5 or so (the status does not change, staying "up to date"), and does not occur with 40 or so selected images (the status changes to "< mixed >" and then after a pause changes to "up to date" after the disk accesses stop).
I have not tried LR 3.5 RC to see if this bug is still there. I am on Macintosh and have "Automatically write changes into XMP" set.
Can someone try to replicate this? I assume it is not particular to my computer, but can't be sure.
Help get this topic noticed by sharing it on Twitter, Facebook, or email.