I am referring to this as a bug because the splitters/mergers are the only thing that do not follow the normal snapping pattern, even when compared with all the other logistic items like conveyor poles and conveyor lifts.
"Normal" Behavior: when holding CTRL and placing an item that is aligned on one dimension on the foundation grid, it increases the aim tolerance for moving the item off the line, but still respects the grid on the other dimension, moving in grid increments
Splitter/Merger Behavior: It will snap on one dimension like the above situation when holding CTRL, but differently, it will no long respect the foundation grid on the other dimension when moving it around (effectively moving like a slide rule)
I do realize this behavior assists with working around minimum belt lengths for some people, but it really feels like that (at a minimum) conveyor poles and lifts should behave in the same way, regardless of which one changes. It is annoying to deal with different components of the item logistics system respecting the foundation grid to different levels, because 1 can through everything else off.