Normal or desireable? probably not. normal for fusion, yes.
Somehow you got the t-spline body turned inside out when you where manipulating it. I'll have to admit I hadn't seen someone do it on accident before. I've requested before that we be able to have a different color for the back face of a t-spline. AD's responce was that they didn't see why anybody would want that. gaaa.
Anyway, since the flip normal tool is a surface tool, it wouldn't be expected to work on a solid body (in the context of fusion. in some other programs, yes). Doing anything that converts it back to a surface body will allow the flip normal tool to work, not just unstitching. like poking a hole in it while in patch space for instance.
As your finding out, surfaceing isn't one of fusion's strong suits.
