Reproduction steps:
1. Create a new project
2. Go to “Preferences… → General”
3. Change the “Editor Theme“ parameter to “Light“
4. Grab the “Hierarchy“ and “Scene“ window splitter
5. Drag them quickly from one side to the other
6. Observe the Editor

Expected result: Dragging doesn’t create a temporary dark area
Actual result: Dragging creates a temporary dark area

Reproducible with: 2023.1.0a1, 6000.0.54f1, 6000.1.14f1, 6000.2.0b13, 6000.3.0a3

Reproducible on: Windows 11 (24H2) (user’s), Windows 10 (22H2)
Not reproducible on: macOS Sequoia 15.5 (M3 Pro)

Notes:

* Reproducible with the “Direct3D 12“ graphics API
* Not reproducible with the “Direct3D 11“, “Vulkan“, and “OpenGLES3“