Hi, Dexter. It is a known issue. Consumption is a rational number. On the server side we do calculation and rounding on whole fleet`s consumption. On the client side we don`t know how much units you will select, so we need consumption per unit and we do calculation and rounding per 1 unit. When the consumption is low and amount of units is high client side calculation gives another consumption and wrong free space.
We did some changes on this issue, so it happens mostly on spy probes on big distance. When it happens just adjust amount of resources according to the message.
In your example actual consumption is higher by 68 vespen, so the actual capacity is less by 68.
UPD: I solved issue