Hi there...
The simplest reason why the virtual sliders work differently in this case is because of the the consistency of persistent pressing of a touch screen and the inability to press two areas at the same time. While the touch screen technology has improved substantially over the last many years, it is very possible for a "blip" to happen where the touch screen thinks the user has lifted their finger and replaced it again. This would result in a "released" event and possibly another pressed event...which is not desired. We don't really see that much now, but in the early prototypes of Eos it would sometimes be a problem. Most of our virtual controls were designed around the idea that a user would be using a touch screen with them, so we never changed the behavior. Also, since the touchscreen (or using a mouse) you are only able to press one bump button at a time, it also limited what we could do with the sliders. Anyway, we decided to just make the user press the virtual bump button twice to achieve the effect of a physical press and release of a bump button. This makes it a little difficult to do a quick flash of a light, but for most operations, ensures the user can achieve the behavior he or she desires.
As with almost everything on Eos and Ion, we continue to look and evaluate decisions we've made, and at some point we may decide to have the physical and virtual buttons behave the same, but for right now, we think this gives the users the best options for controlling the submasters.
-D
www.etcconnect.com