In Stable, when calling applyEdit multiple times before the first one is complete, subsequent calls are rejected, until the first edit is completes. This allows you to make the assertion that if an applyEdit succeeds, there should be one, and only one, onDidChangeTextDocument change event containing the edits that were applied.

This is not true in Insiders -- both applyEdit calls will succeed, and there will be multiple onDidChangeTextDocument events raised.

Attached is an example extension that has one command -- minibash.concurrentBash that will show the repro.

Expected Debug console output w/ Stable:

1: Applying Edit: 0,0, text: 'O'
2: Applying Edit: 0,0, text: 'DRENG'
Doc changed with 1 changes
1: Applied Edits
2: Applied Edits
2: Failed to apply edits
Failed

Output w/ Insiders:

1: Applying Edit: 0,0, text: 'M'
2: Applying Edit: 0,0, text: 'RRGAOCOQ'
Doc changed with 1 changes
Doc changed with 1 changes
1: Applied Edits
2: Applied Edits
saw multiple edits
saw multiple edits
Failed

To run this:

1. open the extension sources, and F5
2. create a new empty document (or open existing one)
3. Run Minibash: Concurrently Bash
   Minibash.zip

Note, that if you remove the return false; on line 69 in doEditsUntilBad, you'll see that Insiders will happly apply 1000 edits. Stable does not; it immediately fails on the second edit (As expected)