Forge Version: 10.13.4.1558
SignPicture Version: 2.8.0

Placing a signpicture in the world causes chests (and similar items) to lose their shading, particularly items that are placed after the signpicture was already placed. I first noticed this bug when placing objects from the Decocraft mod, however I am able to reproduce it with only SignPicture installed using vanilla chests. The easiest way I've found to reproduce this is to place down a few chests, then place a signpicture, and refresh with F3+A. This may be the same issue as #49

I know I am using a very outdated version (I am building a world using some mods that have not been updated past 1.7.10) so I really don't expect a special update to such an old version to fix this issue. However, I am making this post with the hope that there may be something on my end I can do to fix the problem. Any help is appreciated!

Chests before placing sign

After placing sign

I confirm the problem.
Ran through all the modpack (165 mods) and sure enough, this glitch with glowing tiles (it affects not only chests, but a bunch of other blocks (including mods) caused SignPicture.
Please, could you (@Kamesuta) fix this glitch. It is quite stressful during the game and distracts from the gameplay.

Unfortunately, this mod is not actively being updated at this time. It may be merged if someone makes a pull request, but who knows.

残念ながら現在このModは積極的な更新は行われていません。誰かがpull requestを行えばマージされるかもしれませんがどうなるかはわかりません。

Of course, it's sad to read this, but I understand you. We'll have to find a solution to the problem ourselves.
In any case, thank you for your quick response.