[BUG]

Environment

• Platform (select one):
• [ ] Anthropic API
• [ ] AWS Bedrock
• [ ] Google Vertex AI
• [x] Other: Claude Code
• Claude Code version: v1.0.74
• Operating System: Windows 11
• Terminal: cmd

Bug Description

Using sooperset/mcp-atlassian on a jira project that needs additional_fields for create_issue using claude code I cannot get claude code to sent the additonal fields as dictionary and not as string:

Example MCP call:

mcp-atlassian - jira_create_issue (
  project_key: "ABC",
  summary: "Title of the Ticket",
  issue_type: "Bug",
  description: `Description`,
  components: "PROJECT_X",
  additional_fields: `{
    "customfield_10080": { "value": "ABC" },
    "customfield_10082": "TRACKER-1234",
    "parent": "ABC-123",
    "customfield_10026": 3,
    "customfield_10676": { "value": "Patch" }
  }`
)

Giving this to claude4 through github copilot chat, it just works, but it does not matter how i specify the right mcp call, it looks like claude code does not like nested objects in mcp calls.

Steps to Reproduce

1. Setup https://github.com/sooperset/mcp-atlassian
2. Have a Jira Project which needs additional_fields throgh the api too
3. Call the jira_create_ticket command through mcp

Expected Behavior

Ticket was created

Actual Behavior

Error since additional_fields is passed as string and not as dictionary/object

Additional Context

Example above, can be reproduced on latest claude code version. On Github Copilot using GPT5 oder claude 3.7 or claude 4 it just works.