For precise circular orbits the Apoapsis and Periapsis start to move around, vertical speed displays unespected values and it can get quite distracting to the eye.
In this case this is not precise enough to show the weirdest effects, but if you use the RCS to adjust it a bit more you should see the Apoapsis and Periapsis indicators start to blink and teleport
EDIT When I finished the orbit it was 99.3 99.3 and it looks like it's 99.3 99.1 in the sandbox, I tried warping speed (the warp with phisics) and the orbit is getting lower and lower, can't guess why
@PhilipTarpley I think the problem may be related to this bug, so maybe the most efficient thing to do is edit that bug report adding:
With Fast Forward atmospheric effects can appear at higher than 100km Droo's orbits
My guess is that the value needs to be rounded because even showing up like a 0 it may have values in the 1e-4 range.
Another approach could be making planet limit when the value is lower than 1e-4 and force it to 0 after that.
And another approach could be making time warp calculate approximated (to improve the performance) drag effects in order to make the game more realistic, making satellites deorbit after a couple of years. This is my favourite solution but may end up with more complex gameplay.
The perfect solution for me would be a switch in settings with options 1 or 2 by default and the possibility of changing to 3, for "Hardcore" careers and a more realistic sandbox option