It’s by design. Now you can calculate volume per bar by calculating the difference between them. Plus it matches the volume you get in [Trade] mode.

Did you know that if you have M1 data, and you use a larger BarPeriod than 1, then Zorro discards all of the volume data in between each bar? For example, if you set BarPeriod to 5, Zorro discards four fifths of your volume data.