Oh... you are right, spacing option it's not working well when the spline is not normalized. We didn't know this bug
Please, use this workaround to fix it:
1.- Set in the spline "Interpolation->Steps" value to 0
2.- Apply a "Normalize Spl." modifier using "Seg.Length" with the desired spacing
3.- Use Creation Tools->In Vertex Positions
I just found the problem in the source code and fixed it. The patch will be included in the next beta release.
Sorry for the inconveniences.