System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 2070 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 471.68

Blender Version
Broken: version: 2.93.4, branch: master, commit date: 2021-08-31 09:23, hash: rBb7205031cec4

Short description of error
performing undo operation results in loosing render slot images, different from "slot1"

Exact steps for others to reproduce the error

1-render an image on a slot different from "slot 1"
2- press ctrl-z to undo to see the render disappear from the render slot.

This is a problem because the whole point of having multiple slots is to be able to compare before and after changes in the scene.

thank you