In Batch Rename when you sort by EXIF Date, the first file is out of sequence.

In the example above K5__4303.PEF (Pentax K-5 raw file) is later then the other files below it. This is my second attempt. I'd already untagged K5_4304.PEF which was the original out-of-sequence file, then it moved to K5__4303.PEF.
Bug does not occur if you use EXIF Date (descending) order, but unfortunately you can't step by -1, so the renumbered files will be in the reverse order
Dan