On reading the release notes fro 3.4.1 more carefully, I see that another really annoying little bug has indeed been fixed in this release.
This is the one where LR would not save your colour noise reduction settings properly in a Snapshot or a preset. I mentioned this one ages ago, too, and it was the same in LR 2 as well. The scenario was - supposing you create a series of snapshots as you edit, 1, 2, 3 etc. If colour noise reduction was set zero in snapshots 1 and 2, and then you set NR to say 25 and created snapshot 3, if you then switched back to snapshot 1 or 2 for comparison, on returning to snapshot 3 NR would be back to zero again. This was infuriating, because it was easy to miss that this had happened if the NR was just one of several other edits.
I had a go with this last night, and it seemed to be working properly at last.