What I expected to happen: The placed "Sea Lantern" blocks would illuminate the vertical faces of quartz and stone evenly and consistently.

What actually happened: As visible in the screenshot, the vertical faces are not evenly illuminated, but instead have jagged, dark regions. This issue is most pronounced at nighttime. This issue often disappears if the dark region is approached by the player, but this is not consistent behavior - the dark region will sometimes persist even if approached. The behavior persists even if the player logs out and logs back in (this bug was seen on Minecraft Realms).

Further info: I did a bit more testing, and I found that only two of the four faces of the structure had this issue. I then found that the two affected faces WERE ON CHUNK BOUNDARIES. The adjacent chunks were empty (only air blocks). When I placed blocks on the other side of the chunk boundaries, the issue disappeared for the chunk (16*16*16 area).

Steps to reproduce: Build structure shown in screenshot, and wait until nighttime. Disabling smooth lighting makes the issue more pronounced (the jagged edges can be seen distinctly).
EDIT: 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.