P: Sort by capture time should use filename when times are equal

"When I look at the exif data, capture time is only shown to a resolution of one second."

Note that in LR 2015 / 6, LR will not show fractional seconds for what it displays as "Capture Time" or EXIF "Date Time Original". It will show fractional seconds in the IPTC "Date Created" field. And it will use the fractional seconds for sorting in Library view. Very confusing.

I don't believe this matters for the Pentax K-5 II, which doesn't appear to record fractional seconds (at least in the samples I downloaded).

As far as this bug report is concerned, everything ultimately came from a digital camera. There are some files in my library that were created by lightroom's hdr and panorama features, but they share the shutter time of the parent image in the exif.

I was trying to solve another problem, so I didn't document things as well as I should have but I think that the groups that were out as groups may have had odd file creation times, possibly from copying a directory tree from one drive to another.

"I had whole blocks of photos that were out of sequence by months."

That is almost certainly a different issue than the one described here. Did the problem files come from a scanner or from a digital camera?

I was just sorting files to update one catalog with recent edits in another catalog, and not only were photos taken in rapid order out of sequence, I had whole blocks of photos that were out of sequence by months.