It's probably intentional. They're MTB components and being able to quickly go through the gears would be helpful on trails. Some shifters allow for the same thing when shifting up as well. I just did a little bit of searching and haven't really seen it noted as a feature, but I did see quotes like this
You've always been able to grab more than one gear with the thumb lever (lower lever) on RapidFire Shifters. With RapidFire Plus you can now shift two gears with the release lever too.
Which definitely points to intentional.
On the sram site for the X4 shifters one of their main advertising points is that is has "1:1 actuation and every unit of cable you pull moves the derailleur the same amount."
So you're just pushing two shift lengths of cable through when you depress the lever fully on the right side...if that makes sense :/.