Error in verification when copying to encrypted USB drive

[jetico1]

We (Jetico company) are developers of encryption software BestCrypt Volume Encryption.
We have received a complaint from our customer - he encrypted a USB drive and then copied files to the drive, with the option "Verify".
During the process, TC reports that some files are different.
One may assume that the problem is related to our encryption, however, there is additional information that makes us doubting:

1) copy the same files without verification, and then - use the "Verify checksums" for each file - no errors
2) copy files with verification and, as soon as the error appears - compare the files by content - no errors
3) compare the "different" files with third-party tools and with our internal test utilities - no difference

Also, the results of additional tests that were performed to diagnose the problem:
1) copy files to internal encrypted volume (not USB) - no errors
2) copy files to not encrypted USB - no errors
3) change buffer sizes in Configuration-->Copy/Delete - no difference, the errors still happen

We do not know exactly that there is a bug in TC.
Please think about the operation and let's try to understand what was happening.
Please explain in detail (to our developers), how the "Copy and verify" operation works exactly.
We read the information in TC Help, but it is not enough.

[Hacker]

Moderator message from: "Hacker"

Moved to the English forum.

[ghisler(Author)]

By default, Total Commander copies the file with Windows function CopyFileExW. When "Verify" is checked, Total Commander opens the copied file with the flags
FILE_FLAG_SEQUENTIAL_SCAN | FILE_FLAG_NO_BUFFERING | FILE_FLAG_WRITE_THROUGH
Without the second and 3rd flag, Windows just reads the data back from cache, so no verification is done that the data was actually written.

You can tell the user that using "verify" doesn't make sense when copying to an encrypted container, only when writing to a physical disk.