The issues you bring up are not limited to surfaces, or even to just lofts or splines.
The red origin is the sketch origin. You can't really do much with it except use it as a reference for sketch horizontal/vertical, scale about it using the sketch modify tool, and maybe a couple of other things. By default, it is placed at the projection of the part orgin onto the sketch plane, but there are times when it can move, such as when using the sketch modify to move a sketch, and when copy/pasting or deriving sketches.
You're right about the numbers in the property manager showing distance from the sketch origin, even though you cannot dimension from the sketch origin. I can see why it might be a bit confusing, but I never worry about it because I never use the numbers in the prop mgr except to tweak the X-Y position of a particular point by the spin increment.
"T Bennett" wrote in news:bg6sdm$lq1tf$ snipped-for-privacy@ID-183945.news.uni-berlin.de:
modeling is a