The wonderful thing about this site is that it is a resource to many. It matters less that you refused to perform suggested procedures, like moving your aircraft slightly and reporting on those results, than the fact that the problem was presented and those solutions were offered, because people that Google "tcalcx" and rely on this thread for resolutions, will not have the benefit of tailored replies.
It goes without saying that TcalcX works as expected, it was created to help developers by one of the admins here and we are obliged to support it. After many, many hours of placing scenery objects, we learn that a joystick must be centered to use slew mode, otherwise the slightest deflection will prevent the vehicle from remaining stationary. The little red coordinate numbers scroll away, exactly as you describe, even if there is no apparent motion. That is what this situation resembles and that is the valid solution: zero the stick. Now, we understand that may have already performed the suggested solutions without telling us the results and therefore this is a new and unique issue. Luckily in that regard, as you've reported, you've overcome it with slewmaster.
For my own, very precise topography surveys, I do not use helper applications, I use the avatar in slew mode and I calculate an allowance for the vertical offset, it helps me to avoid blaming other developers and softwares for my oversights.