Odd behaviour when just syncing a date string

We're using the LSP library in combination with a WebSocket connection and the JSON RPC integration.

In the frontend, we have a monaco editor running connecting to the LSP. When just pasting a date in the format yyyy-MM-ddTHH:mm:ss, e.g. 2026-11-14T13:00:00, it seems like the JSON deserializer parses the string as a date and within the sync handler, we receive a date in a new format (see below).

This is the outgoing message:

{
  "jsonrpc": "2.0",
  "method": "textDocument/didChange",
  "params": {
    "textDocument": {
      "uri": "inmemory://f6eea487-d551-4046-ada9-9bd285336889/585c22d8-fe2d-4260-865b-1f9bef806c07/2937aaba-b860-4a01-8613-51dbbf0b2f3d",
      "version": 3
    },
    "contentChanges": [
      {
        "range": {
          "start": { "line": 6, "character": 0 },
          "end": { "line": 6, "character": 0 }
        },
        "rangeLength": 0,
        "text": "2026-11-14T13:00:00"
      }
    ]
  }
}

This is what we receive in the backend in TextDocumentSyncHandler.Handle (no user code running in between):

I could not find a way of configuring the default date parse handling for the incoming notification handler.

Does anyone have an idea of how to deal with this issue?

Many thanks in advance!

Start at TextDocumentSyncHandler.Handle and trace the JSON-RPC notification deserialization used by the incoming handler. Reproduce the issue with a pasted yyyy-MM-ddTHH:mm:ss value and compare the received text with the outgoing contentChanges payload. Done means the behavior or configuration path is documented and covered by a regression test.