I got the answer from the other bug application, that: "Not a bug. One volley can shoot only one group.".

But the thing is that at if there are 2 very small groups and Giga has 6 volleys, so he will shoot not one valley to one group, but all valleys to one group. In other words, there are no difference Giga has 6 or 1 volley.

In Characteristics this parameter is named "Attack per shot". So, in these terms, one shot per only one group.

as I understand "The number of shots per volley" this characteristic means how much different groups of an enemy can be attacked at the same attack. 
For example, ships, that have big numbers of shots per volley:

The Needle Tree,
Cruiser,
Space Wander.

They can shoot multiple groups of targets.

Also, the Damage per round === Attack per shot * The number of shots per volley * ratioCorrections

Or I misunderstand this characteristic.

Thanks for the patience. I got the answer. Right now I know what does it mean "number of shots per valley". It's more related to the ability to do mass attacks.