Here is a video demonstrating the issue:
Link
I have attached the world save used in the video that I have tested a setup in multiple times with the same result. I have not included a log file as I see no information contained in the log related to belts or circuit conditions, and the issue does not cause corruption or crashing.I have not attempted to use a logistic network condition in place of a circuit condition, nor attempted this on a straight belt instead of a corner.
I have performed an advanced search using the phrase '+belt +circuit' and I have not found my issue mentioned elsewhere. No mods are enabled (other than the default Base Mod).
On a side note, I originally typed up a more in-depth description of the issue, but when I clicked 'save draft,' the draft was not saved and I was brought to a login page instead. I lost all that I had typed up, and I would rather not retype it. The issue saving has not occurred a second time, and I am certain that I was logged in before clicking save draft.