Chisel Version: "MC1.12.2-0.2.0.31"
Block: Cobblestone, Big Tile "#6663/7"
Enigmatica 2 Expert: 1.4
Forge: 14.23.4.2751
FoamFixCore: 7.7.4
BetterFPS: 1.4.8
Optifine: 1.12.2_HD_U_E2

I noticed this happend when I logged into my SP world just now. After seeing it, I logged out, then in again. The glitch was still there and I took the screenshots. When I relogged again (I did not restart) it disappeared.

I did not get an image of this, but it appears as though the glitch only appeared on the top of the blocks, and only on blocks with connected textures all the way around. Blocks next to another kind of chiseled block, or at the edge of a platform, did not have the coloration. It appeared that all blocks in the world had the issue.

I do not have screenshots of this, but I noticed a few days ago that the same thing happened to Bricks "#6665/0", but only to the underside, and the coloration was purple instead of yellow.

Its not the biggest issue for me because I don't go nuts about aesthetics, but I figured you guys would want to know!

Can you reproduce this without Optifine?

Hmmm, at the moment I am unable to get it to reproduce at all.

I'll see about making a creative world with a whole bunch of chisel blocks and see if starts happening more consistently.

I have just gotten what I believe to be the same bug on Crackpack 3. I don't know what causes it, but I thought I'd post this here so it's known that it still exists.

I have installed the latest version of Optfine 1.12.2 on top of Crackpack 3

If it only happens with Optifine then nothing has changed.

other than it's purple. (just jokin)
It's also not on every block, only the ones on the south edge of the connections. And it's disappeared after I relogged just as before

Sounds like the official solution is to either not use Optifine or just relog.

To be clear, I never saw this again after the first few times I saw it. This is one of those mysteriously elusive bugs that doesn't really hurt anything, but always makes you wonder where the code is going wrong. With the low occurrence rate, you can probably just mark as not reproducible and close it? At least people Googling will know it doesn't happen often.