Thanks for the response - I'm unable to attach the world because it's too big (192MB compressed, versus the 10MB upload limit).
I found out some additional info about this bug. It only occurs when the vertical face is on a chunk boundary. To replicate, create a large vertical wall on a chunk boundary (on block 0 or 15 of a chunk's x or z coordinate). Then place a sea lantern somewhere in the middle of the top of the wall. The chunks across the chunk boundary must be empty of blocks to replicate this bug. Then wait one or more day-night cycles while staying at least a few chunks away.
Hello, this bug is not resolved, but it appears to be marked as such