Here's the explanation. It's all to do with the fact the sliders can be used to control several 'sets' of values. They will never initially match the 'current' values when you jump between the set of settings that the sliders currently control, for example changing from the overall part volume balance to the organ drawbars.
When you move the sliders, nothing happens until you move the slider *past* the position that matches its current value. Then it 'picks it up' and changes the value along with the slider movement. This applies whether you have to move the slide up to pick up the value, or down. So as you say, the screen always shows the current values, but the physical slider positions probably won't match.
The reason for this is that otherwise, when you touched a slider, the current value of the parameter would suddenly jump to match the slider position. And that's not likely to be a good result.
The same principle applies to the knobs.
This is quite a common way of working in all makes and models of synths / keyboards. *Very* occasionally, manufacturers have used motorised sliders to move them to match the current value when loading a registration. The modern alternative is what's known as 'endless' rotary knobs which use LEDs to indicate the current value.
Incidentally, the sliders normally control 3 'sets' of values and you can customize the values that each one controls through the live control menu. When you have an organ drawbar in any of the L or R voice slots, an additional 'set' of values is added to the slider display for each voice to control the drawbars on that voice. So you can see that if you were layering drawbars on say R1 and R2, when you changed the slider assignment between the two voices they would never line up to start with.
If you are just sticking with one voice, the solution to keep them and the screen in sync is to move all the sliders all the way out, then move them all all the way in, then dial in your particular drawbar settings as required.