The calculate volume tool only works on a single target polygon. If multiple polygons are present it's quite tedious to calculate one-by-one and manually sum the totals. For example in a bathy survey of a channel it's common to have different areas of accretion that need to be calculated.
There doesn't seem to be an image upload feature. The exact tool is "Analyze Volume Terrain Model".
Can you post a screen shot of the volumes tool you're using? We have multiple for a wide variety of use cases.