To see what will happens, I tried to create a loop in a pipeline. I expected an error notification from K-3D, but did not get one (there no crash too, an that was good).
Then later I saw the page:
Ok, now I know why I did not get a message from K-3D. I understand the rational behind this (no crash), but I believe raising an alert box and refusing to apply an accidental loop, could be a better option. Better an alert so that the user know he/she did something wrong, than silently doing something else which the user will not predict.
Note aside: this pipeline oriented design is clean, that's nice.