If you can reproduce the bug in Paraview then maybe it’s developers can fix this issue. If they don’t use this widget then you might need to take care of this issue yourself.
In 3D Slicer we tried to make use of VTK widgets for about a decade but they had so many issues (not just superficial issues like this one, but fundamental problems, too) that we gave up on them and implemented similar widgets with simpler and more efficient design. We have a spline widget that works well (for example, does not have this particular bug). If you need interactive pointset, line, angle, open/closed curve, or plane VTK widgets then you can use the implementation in 3D Slicer’s Python environment.