Persistent MDC File Corruption Issues in Cursor: Metadata Loss and Duplication

Support Bug Reports
1

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

Since the very first day the Cursor custom rules were introduced in MDC format, it has been impossible to properly edit these files inside Cursor. From day one until today, nothing has changed. The moment you modify the metadata, Cursor either wipes the entire metadata block or duplicates chunks of it.

You’re forced to rely on other extensions or full IDEs just to work with MDC files, because Cursor keeps tripping over itself every time.

Steps to Reproduce

You have to sequentially edit multiple MDC files and have to impose different requirements on them to see what’s going wrong. Once you do that, you’ll quickly notice that at some point there are issues with the MDC headers: they get completely deleted and reset, or new content is added to a rule even though the old content really should have been removed. I suspect this is happening because Cursor itself doesn’t reliably detect that the MDC headers have been deleted; it then tries to add content at a specific line, without realizing that the previous content is still there or that the structure has changed, which leads to these inconsistent headers and stale rule content.

Expected Behavior

Can edit .mdc files without bugs

Operating System

Windows 10/11

Current Cursor Version (Menu → About Cursor → Copy)

Version: 2.1.6 (user setup)
VSCode Version: 1.105.1
Commit: 92340560ea81cb6168e2027596519d68af6c90a0
Date: 2025-11-20T03:38:22.386Z
Electron: 37.7.0
Chromium: 138.0.7204.251
Node.js: 22.20.0
V8: 13.8.258.32-electron.0
OS: Windows_NT x64 10.0.26100

Does this stop you from using Cursor

Yes - Cursor is unusable

2

Hey, thanks for the report. To help us investigate, please share:

  • A concrete example - before/after screenshots or file contents showing where metadata is deleted or duplicated
  • Which Cursor feature you’re using when this happens (Ask, Agent, Custom mode, or Inline Edit)
  • Minimal repro steps - for example: “Open file A.mdc, ask Agent to add rule X, then open file B.mdc and ask to add rule Y”
  • The request ID - after the corruption happens
  • A sample MDC structure - what does the header of a typical MDC file look like in your setup?

This will help the team understand exactly where line tracking is breaking.

3

In the current Release I can not re-produce it anymore. Maybe it was fixed or it was related to conflicts with this extension enabled:

If I can re-produce I will post details. Thank you for your time

1 Like
4

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