Ok, if we really want to get technical here, your issue is even worse than stated. Reason being is there is a lot of flex going on, the cross slide itself has some give, even your toolbit itself has some flex (which often can impact your finish). In fact, even they ways themselves will flex and buckle during operation (you don't see it with your eyes).
The problem is rigidty, rigidity, rigidity. And is one of the reasons it is so dangerous to do a parting-off operation with a mini-lathe.
Each lathe has a different amount of flex when cutting, and even the same model will be out of tolerance to one another, simply due to difference in tightness of gib strips, length of toolbit, and other factors.
Here is the good news though, it doesn't matter too much once you've got the FIRST turning cut done. One thing all lathes have in common, is turning your dial 1/4'th of a mm for example, should advance the cut exactly that amount in comparison to the other cut previously. It doesn't matter how much give/flex there was previously. Each notch turn on the dial should be consistent in COMPARISON to the previous operation. This is because you are using the same machine and set-up.
Does this make more sense?