By default a full inventory scan(software) is ran once in a rolling 24 hour period, all subsequent scans do not contain software information just hardware. You can force a full scan at anytime as you did to get the full software scan. The 24 hour period time frame can be modified to every login or every X days. This setting is controlled under configure--services--inventory-software. You can also create a custom script that does a full inventory scan that way you can schedule a task from the core so you don't have to manual modify the clients command line.
Thank you, I did not know that. It was driving me nuts.