File size problem when extracting from split RAR files in DOpus

I'm having a problem that I hope I can properly explain. Basically, I have a folder that contains a group of 51 split RAR files as such:

OldHardDiskBackup.rar 190MB
OldHardDiskBackup.r00 190MB
OldHardDiskBackup.r01 190MB
OldHardDiskBackup.r49 103MB

My problem is that the .tib file (Acronis True Image Backup) contained in those RARs should end up being listed as the correct 9.43GB when I open the OldHardDiskBackup.rar file in DOpus. But for whatever reason, DOpus ends up displaying the .tib as having a file size of "8,191 PB" (with a comma and not a period). Due to this, DOpus ends up trying to extract the file and can never finish since the file isn't as large as DOpus thinks it is.

I managed to extract the .tib file by installing a demo version of WinRAR, which showed that the .tib file was 10,126,163,968 bytes, and properly extracted it to 9.43GB.

I just wanted to mention this here because I'd rather not have to install WinRAR solely to access this one backup, and thought that there was must be some sort of bug in the RAR plugin that DOpus uses that causes this problem.

Is there some setting or something I can change I can do to make DOpus be able to work with this set of split RARs correctly, or is this really something that needs fixed with DOpus itself?

I hope you can help me with this.

If you go to Preferences / Zip & Other Archives / Archive and VFS Plugins and configure the RAR entry there, there's an option to switch between using UnRar.dll and 7z.dll to unpack RAR files.

You could try toggling that to see if using the other DLL makes a difference. (It's best to restart Opus afterwards, via File > Exit Directory Opus, to make sure the switch-over happens.)

(Adding to that, I've just tried with a split RAR containing a single 15 GB file, and the size was reported correctly, so there may also be something unusual about the RAR itself. UnRar.dll and WinRar are both by the same people, but I think also do have some differences as well. They may also be different versions.)