I've already reported this via the official support form, but I wondered whether anyone else can confirm this behavior.
I seem to have discovered a problem in creating zip files with the Opus 'Add to Zip' function.
What I'm about to describe here applies when actually creating a new zip file and when and only when a password is specified for the zip file.
I've made no attempt to discover what happens if files are being added to an existing zip file, but I can say that this problem does not exist if no password is specified for the zip file.
If more than one folder is selected for inclusion in the new zip file and one of these folders or a subfolder is empty, the resulting zip file is unusable.
Trying to extract the contents of the zip file in Opus results in nothing happening.
Trying to extract the contents of the file in PowerDesk results in a message that access to the file is denied.
Trying to delete the file in either Opus or PowerDesk results in a message that the file is in use by another program.
These symptoms exist until Opus (not just the lister) is terminated.
If Opus is terminated and restarted, attempting to extract the contents of the zip file in Opus still does nothing.
Attempting to extract in PowerDesk now produces a message 'Error in ... archive directory'.
After the termination of Opus, the bad zip file can be deleted in either Opus or PowerDesk.
Also worth noting is that if one single empty folder is selected for inclusion in the zip file these synptoms do not occur. The empty folder has to be one of multiple files or folders selected to cause the described symptoms.
I don't know if this is a problem in Opus or some weird problem only on my system. I'd think it possibly some problem inherent in zip files, but if I do the same zipping operation in PowerDesk, the contents of the resulting file can be extracted with either PowerDesk or Opus.