It’s almost like the original programmer assumed that the only time a control point would be dragged is when starting a new segment. I hope it’s actually an easy fix. I know it was discussed at some point, but that might have been before you took the reigns of development.
You have to if you want a curve to adjust to different measurement sizes. Unless of course you used the Fixed curves / splines which in theory are fixed to points that are formulzied.
It should be an easy fix once I figure out the exact place the handle point is being set. It’s this complicated coreographed dance between the VToolSpline / VAbstractSpline, the spline dialog, the spline visualization, the VControlPointSpline tool, the VScaledLine and SceneRect graphicstitems, Undo commands and how all the parts are being tracked and painted while you are dragging scene objects. Unfortunaley there’s nothing saying “Here’s where we track the control handle length”. 
Most likely… otherwise I would have fixed it as I generally tend to do. Again it’s something I probably noticed early on, why I just avoided dragging the control handles during creating a curve, and just forgot about. At the time I probably had no clue how much of anything in the code worked. I’m just kinda of surprised it’s gone this long without a Github issue. 
Funny thing now after playing with the tool and realizing the length is created when you drag… even if it’s an infinitesimal amount of time between press & release I can only create a line… or drag the handles. 