Steps:
1) Start a new game (in sandbox mode so that you have immediate access to splitters)
2) Place a splitter
3) Change it's input or output priority. The arrows that usually indicate the priority will not appear in the world, but will appear in the splitter tooltip.
This does not seem to happen for some earlier saves that already have priority splitters in them. If the earlier save does not have any priority splitters, then this bug does seem to occur.
The priority splitter functionality is not affected, only the graphics.
