[Shaders] Custom sky rendering issue when using shaders

[CeelB-2055440]

Description of Issue

When I use optifine with a resource pack that makes use of customs skies (lets say JohnSmithLegacy), then the rendering goes wrong when optifine internal shaders are enabled.

Steps to Reproduce

Enable internal shaders
Enable custom sky
Enable a resourcepack that makes use of it.

OptiFine Version

OptiFine HD U J2 pre1 (1.21.3)

Installation Method

Included standalone installer

Fabric/Forge Version

N/A

OptiFabric Version

N/A

Other Installed Mods

N/A

Log Files/Crash Reports

latest.log

F3 Debug Screenshot

Prior Testing

In vanilla there is no problem.
When shaders are disabled, there is no problem.
When custom sky is disabled there is no problem.

Additional Information

(You can ignore the time set 18000 (OF is set to day only))

[CeelB-2055440]

Problem continues to exist in version: OptiFine HD U J2 pre2 (1.21.3)

[CeelB-2055440]

Problem continues to exist in version: OptiFine HD U J2 pre3 (1.21.3)

[CeelB-2055440]

I have found that it doesn't work with any shader pack.

[schrodingerspsycho]

Problem continues to exist in version: OptiFine 1.21.3_HD_U_J2_pre4 (1.21.3)

[schrodingerspsycho]

Problem continues to exist in version: OptiFine 1.21.3_HD_U_J2_pre5 (1.21.3)

[ZenithRogue]

"Internal Shaders" are not actually supposed to be used. They are just there for debugging purposes

[sp614x]

Renamed internal shaders to debug shaders.

[schrodingerspsycho]

Problem continues to exist in version: preview_OptiFine_1.21.3_HD_U_J2_pre6
As it was stated, the problem affects all shaders, not just debug/internal ones, for example I use Sildur's Enhanced Default v1.171 Fancy, they do break in OF for 1.21.3 and do work fine with 1.21.1-OptiFine_HD_U_J1

[schrodingerspsycho]

Problem continues to exist in version: preview_OptiFine_1.21.3_HD_U_J2_pre7
+some buggy skybox culling has appeared: