I really like the changes to the 0.16 non-robot rail building interface, in particular, the changes for manually placing curved rails. Finally, I'm able to join perpendicular lines without approaching the target one rail entity at a time!
However, there is a really, really annoying behavior in the 0.16.1 implementation. I'd call it a bug but y'all have me terrified of reporting anything as a bug that might conceivably be working as as intended

Hard to explain concisely but words = pictures / 1000 so: In the above you can see my mouse click actions in that xinput monitoring console (I'd have made it more clear but it inexplicably stops working, if I ask bash to pipe the output of grep to sed! Totally wierd. But that's another bug report....)
I think what's happening here is that the little producer monkey who maps "where is the mouse" to "which kind of rail to build if the user clicks here" only offers straight rail up to a certain distance; beyond that he is only willing to offer the consumer monkeys left or right turns, for whatever reason.
The problem is not "virtual". I should have shown this in the movie, sorry. If I do actually click, once it starts to offer me that curved rail, as shown in the video, it does indeed build a curved rail there.
End result: if I'm zoomed way out and running like hell with my power armor filled with legs, the manual rail builder just keeps building turns I didn't ask for over and over, simply because I ran "too far for straight rail" between mouse clicks.
At first I thought this must be because I am too old to hold the mouse steady. True, but in this case that was not the problem

To be clear, my "idea for an improvement" is: the producer monkey should offer straight rail, or maybe no rail, as applicable, if I move the mouse to a location roughly along the existing rail direction, no matter how far away from the connection point I may move the mouse.