Rendering issues using BackBufferCopy node in 4.4 beta 1

[TanyaPegasus]

Tested versions

• Noticed issue with Compatibility renderer in v4.3.stable.official [77dcf97] but at the time assumed it was my lack of knowledge of the engine and what was possible with shaders. Not present in Forward+ renderer in 4.3 stable
• v4.4.dev7.official [46c8f8c] Noticed issue with Forward+ renderer. Still present in Compatibility renderer.
• v4.4.beta1.official [d33da79] Tested and still present with both renderers.
• Haven't had the the chance to see which version the issue starts at yet.

System information

Godot v4.3.stable - Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3060 (NVIDIA; 32.0.15.6636) - 12th Gen Intel(R) Core(TM) i5-12400F (12 Threads)

Issue description

I have a Camera2D node, and multiple TileMapLayers. The issue seems related to the TileMapLayer which is a child of a BackBufferCopy node. That TileMapLayer uses an additive blend mode, and has a sibling which uses a multiplicative blend.
When zooming out, there are bright lines appearing across the screen, with the rest of the areas appearing as though their additive blend mode no longer applies. Areas behind are darker, so it seems that the mult blend on the lower layer is still in effect.
I tested hiding and un-hiding each layer. The issue was still present whether the mult layer was visible or not.
Issue was still present if I removed the additive blend shader from the first layer.
Issue disappears if I remove the layer form the BackBufferCopy node.
I considered it could be related to the number of scenes I had displayed as I'm using a scene collection tileset source that's quite large, but my reproduction has very few nodes or textures.

I was using the BackBufferCopy for my first attemps at shaders, and didn't check it was still needed when I found a better way, so my project no longer needs this, but still seemed a good idea to report it.
I tried to search through the issues, but none seemed similar enough that I could be sure they seemed related with my level of experience with rendering.

Expected behaviour
4.3 stabke, Forward+
This is what I expect to see:

v4.3_stable_forward.mp4

Unexpected
4.3 stable, Compatibility
Current version if I change renderers. What I saw early on and didn't understand if I was just doing something wrong:

v4.3_stable_compat.mp4

4.4 dev7, Forward+
What my project looks like if I open it in the newer version. beta 1 looks the same:

v4.4_dev7_forward.mp4

4.4 beta 1, Forward+
My minimal reproduction version:

v4.4_beta1_forward.mp4

Steps to reproduce

Add a TileMapLayer as a child of a BackBufferCopy. Have other TileMapLayers below.
Add 400 x 400 tile area to first layer with tiles that are 128 x 128 pixels
Tiles on other layers (including BackBufferCopy child layer) are 1024 x 1024 pixels. Add enough to cover the first layer.
Add a Camera2D node and zoom the camera out far.
Tested with project below and issue first appears when map size is 128 x 128 tiles. 127 and lower doesn't show the issue.

Minimal reproduction project (MRP)

Created with v4.4.beta1.official [d33da79]
renderingreproduction.zip