Pathfinder bugs and artifacts
Pathfinder distorts curves and these distortions create stray points and small vector artifacts when I "slice".
This has been an issue from IL5 (pre-CS and pre-CC), when Pathfinder was first introduced.
Until Adobe increased maximum magnification, it was hard to tell what was happening, but in CC I can clearly see that in Pathfinder, smooth curves distort. My guess is something analogous to mathematical rounding errors in defining the berzier curve.
Sometimes, the distortion is very "squiggly", appears to be introducing the 'QuickDraw error (reported separately), and produces unusable results.
While most of these errors and artifacts are essentially microscopic, and can be minimized by applying pathfinder to oversize art and scaling-down, it is still an issue and can be a serious problem if you're creating art that needs to be scaled-up to sizes where the errors and artifacts become conspicuous.
This is absolutely horrendous when you're designing icons (or like, anything). It's mathematical curves, nothing should change when you merge two paths. Here's a video of how this goes wrong: https://twitter.com/themoenen/status/1215376223695753219