When applying or removing resource packs with core shaders, the core shaders do not get reloaded and instead use the core shaders from the last reload. The core shaders only update after pressing F3+T after changing resource packs.

This also happens if you make an edit to a core shader and reload with F3+T. The change will only show if you press F3+T a second time.

The output log will also be filled with "Double closing program" warnings on reloads (relates to MC-226660).

To reproduce:

1. Download the provided resource pack
2. Make a world with solid blocks in it like stone
3. Apply the resource pack
4.  Observe that the solid blocks are not red
5. Press F3+T
6. Observe that the solid blocks are now red
7. Edit rendertype_solid.fsh in the resource pack and change the fragColor to vec4(0.0, 1.0, 0.0, 1.0)
8. Press F3+T
9.  Observe that the solid blocks are still red and not green
10. Press F3+T
11. Observe that the solid blocks are now green
12. Remove the resource pack
13.  Observe that the solid blocks are still green
14. Press F3+T
15. Observe that the solid blocks are now normal