I discovered this while trying to align individual nodes on multiple paths today. The simplest case to reproduce is as follows:
Draw 3 overlapping paths with three 'sharp' nodes each: Start, (approx) middle and end.
Using the Node tool, select the middle nodes of each path
Choose Align Horizontally: Center and Align Vertically: Center
Observe the center points. Depending on the starting positions of the nodes, they may now be curved instead of sharp, and oddly curved when viewed up close.
In this case, I would expect the nodes to stay the same type (sharp to stay sharp, curved to stay curved). The strange curved behaviour seen in panel 3 attached seems especially wrong though, and currently means I can't use the align tool for this job.
Let me know if I can provide any more info. Thanks!