Oh, I got it now, and also understood a bit more about how ingame works.
So, when Zoom Sensitivity Scaling is on, like in game, you can manually set the sensitivity of the various zoom values. In the Calculator, it also means that the Sensitivity1 space is blank and must be filled with a number that corresponds as the Global Sensitivity. So, if I use Global Sensitivity as 1, I have to manually input 1, if 3, I have to set 3 and hipfire, 1x and 4x scale accordingly, and so on.
When Zoom Sensitivity Scaling is off, like in game, the scaling is done by the game automatically, right? So the Sensitivity1 space is greyed out because the Calculator directly changes Global Sensitivity and doesn't need manual input.
Now, for the Glitch, in my browser, Firefox on Win10, it seems that switching from the sensitivity tab "All" to the tab Hipfire, it still remembers as if there 1 there, and proceeds to calculate on that, even if Sensitivity1 space is empty. Switching to another sensitivity then makes it forget that ghost 1. I can't reproduce the glitch in my phone with another browser instead. I'll try clearing the browser and try with other browsers tomorrow and see if the glitch sticks.