First and foremost consider this:

This is a DEVELOPER oriented channel dedicated to report bugs and suggest features about the libretro core, please do not ask for help. If you need help, go to https://forums.libretro.com/;
The upstream bug tracker is a forum thread, located at https://forum.fobby.net/index.php?t=msg&th=1114;
- Note: As of October 2018, Microsoft email providers (think email addresses ending with hotmail/live/outlook) are rejecting email from the forum. If you want to register an account in the upstream project's forum, consider using another mail provider.
For game-related bugs:
1. First, check if it's already reported on the upstream bug tracker;
2. If it's not reported there, try to reproduce the bug with mednafen;
3. If it's reproducible with mednafen, report it on the upstream bugtracker;
4. If it's not reproducible with mednafen, ONLY THEN should you report it here.
5. DO NOT report Beetle-specific bugs on the upstream tracker.

Description

[Description of the bug]

[What you expected to happen] [Photos/videos of original hardware behavior and/or mednafen behavior]

[What is actually happening] [Photos/videos of the core's behavior]

[Try to bisect and tell us when this started happening]

[If you're using RetroArch, this information is on the bottom left after loading the core. You can do this via Main Menu -> Load Core]

Please specify whether you are using Beetle PSX or Beetle PSX HW.

[List all the core options you have changed]

Please also specify, if reporting a graphical glitch for Beetle PSX HW, your "Renderer" core option setting and your frontend selected video driver.