Every time have a file opened in LibreOffice and forget to close it while my system perform a backup, this file will not be saved, because LibreOffice will not release the file-handle after it has opened it, so every try to copy it will fail.
It would be nicer to release the file-handle, so not to break system accesses to that file. Like all text-editors do it.
Thanks in advance
Jens
99% text editors don’t do that 
- I mean MS Word and other rich text editors on Windows, where 99% of world’s text editing happens (for good or bad, but…). I can’t say what’s the convention on other platforms (I use Windows myself), but here goes consistency of LO behaviour across platforms vs consistency of LO behaviour with other platform tools.
Anyway, your “question” looks not a question, but rather a bug report/enhancement request? then it’s off-topic here.
I doubt it has anything to do with the “file-handle”.
The backup utility can read the open file but it is probably failing because the utility cannot set the Archived bit on the open file to show it has been backed up.
Good backup utilities use Volume Shadow Copy (Windows) which takes a snapshot of the disk and allows all files to be backed up and their Archived bits to be set irrespective of whether the file is in use or not. See Cobian and Macrium.
Get a different backup utility because if yours does not use a Volume Shadow Copy (Google it), or you have not enabled it, your backup is next to useless as LO files are unlikely to be the only files missed.