Long story short: Lr's FFC works not as described. Description tells that only first or last file in sequence is treated as the reference flat field frame, but actually every file is checked for uniformity, and if Lr decides that it is uniform enough to be treated as the reference - it is treated, and the next file treated as photo is corrected using this "new reference" file that actually is a real photo, just not-so-contrasty.
It leads to two issues:
- not all files are corrected
- if there is a file in the middle of the sequence that is not corrected, then files after (in the direction from real reference file) that file are corrupted.
Steps to reproduce:
- do as described in the guide: place a real reference file first or last in the sequence
- have one or more files with low contrast in the sequense
- perform FFC
ER: all files are processed using first or last file as reference.
AR: every file is checked for having low contrast enough to be treated as reference, and in case it is treated - all consequent files are processed using this file as reference, not the first\last.
Attached screenshots: with issue, and with hints where to look at. Take into account that LR processed files from the last to the first, as the reference is the last file in the sequence.
I can not attach photo file that is erroneously treated as reference because it exceeds allowed file size, but I can provide any files in some other ways if needed.