Hello,
I thought the problem would not happen with an installed application on an administrator session on Windows, or occur an error message... to confirm to you that it is possible: a free open source synchronisation software deals with the deleting of bit-locked files.
What "I tell you" is that:
If the partition backup is mount and unencrypted by an encryption file/folder software (not the bitlocker of windows),
Then it might not occur the same problem.
So next time I will try to:
Synchronize the original with the backup,
Apply the duplicate file function of ccleaner on the no-bitlocked backup,
Then mirroring from the backup to the original in the folder set up to bitlock the original upstream folder
If you rethink to this 3 points, you might:
Find out:
that it is quite complicate,
an interesting extend function to ccleaner, not so far from the duplicated folder deleting function,
Suggest a function quite interesting for the purpose of your software, specially if it manage the same found out function on cloud services.
Br,