Is the [WARNING] '--update-of' is unreliable on Windows! message valid while doing .dwm backups after booting from Windows PE \ Preinstallation environmet? In the WinPE, there is no open handles to any files on the host operating system in the drive C:
Reading this section in the wimlib documentation :
Note: in the Windows version of wimlib, it has been observed that --update-of mode is not completely reliable at detecting changes in file contents, sometimes causing the old contents of a few files to be archived rather than the current contents. The cause of this problem is that Windows does not immediately update a file’s last modification timestamp after every write to that file. Unfortunately, there is no known way for applications like wimlib to automatically work around this bug. Manual workarounds are possible; theoretically, taking any action that causes the problematic files to be closed, such as restarting applications or the computer itself, should cause the files’ last modification timestamps to be updated. Also note that wimlib compares file sizes as well as timestamps in determining whether a file has changed, which helps make the problem less likely to occur; and the problem does not occur on other operating systems such as Linux which maintain files’ last modification timestamps correctly.