Toggle between Light/Dark Themes command stops working when using builtin themes such as Monokai

System details:

Positron and OS details:

Positron Version: 2025.10.1 build 4
Code - OSS Version: 1.103.0
Commit: b13dd1ca4803bc04a4a9165395b589b8caf4ab58
Date: 2025-10-14T21:43:42.876Z
Electron: 37.2.3
Chromium: 138.0.7204.100
Node.js: 22.17.0
V8: 13.8.500258-electron.0
OS: Darwin arm64 25.0.0

Session details:

R 4.5.1 (but that's not an issue here)

Describe the issue:

If the preferred dark color theme is set to a custom theme, the "Toggle between Light/Dark themes" command (workbench.action.toggleLightDarkThemes) stops working.

Steps to reproduce the issue:

I have three videos demonstrating the issue.

First, here's how it's supposed to work, where the preferred dark theme and preferred light theme are Positron Dark and Positron Light. Toggling between them is fine and normal:

https://github.com/user-attachments/assets/c29b1812-41e7-4b9a-be1d-202997efac89

If the theme is set to something else (here Monokai), and then toggled, it switches to Positron Light, then Positron Dark, as expected, since that's the preferred dark theme:

asdf

If the preferred dark theme is set to Monokai, though, the toggle command switches it to Positron Light, as expected, but it will not switch back to Monokai (or any dark theme). The only way to get it back to a dark theme is to go into the settings and modify Workbench: Color Theme manually

https://github.com/user-attachments/assets/3dff420a-afa2-496e-b328-bf3da035e372

Expected or desired behavior:

Positron should be able to toggle between the two preferred light/dark themes

Were there any error messages in the UI, Output panel, or Developer Tools console?

Nope, nothing changes in the developer tools console :(

Start at the workbench.action.toggleLightDarkThemes command and the Workbench: Color Theme preference settings. Reproduce the issue with Monokai as the preferred dark theme, then compare the toggle behavior with Positron Dark and Positron Light. Done means toggling from the preferred light theme returns to Monokai or the configured preferred dark theme.