Function calling schema inconsistencies between functionCallingConfig mode ANY and AUTO

Gemini API
1

When passing a tool schema with ANY nested map-like objects are not being returned properly. If I use AUTO, however, it works as expected.

Here’s an example call that does not return the correct function call. Switching mode to AUTO resolves the problem.

I’m not sure why this inconsistency exists. Am I doing something wrong? It seems like a bug in the API.

curl -s -X POST \
"https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash-lite:generateContent?key=$GEMINI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
      "systemInstruction": {
        "parts": [
          {"text": "You are a helpful assistant. Keep responses concise."}
        ]
      },
      "contents": [
        {
          "role": "user",
          "parts": [
            {
              "text": "FIll out a form with form id '\''jobApplication'\'' and entity references '\''person'\'' with keys '\''personId'\'' (12) and '\''personName'\'' (bob). YOU MUST FILL OUT THE KEYS"
            }
          ]
        }
      ],
      "tools": [
        {
          "functionDeclarations": [
            {
              "name": "fillFrom",
              "description": "Fill a form with data from specified entities. Be sure to provide all the required entities with their associated keys.",
              "parameters": {
                "type": "object",
                "properties": {
                  "formId": {
                    "type": "string",
                    "description": "The ID of the form to fill"
                  },
                  "entityReferences": {
                    "type": "array",
                    "items": {
                      "type": "object",
                      "required": ["entityName", "keys"],
                      "properties": {
                        "entityName": { "type": "string" },
                        "keys": {
                          "type": "object",
                          "minProperties": 1,
                          "maxProperties": 1
                        }
                      }
                    }
                  }
                },
                "required": ["formId", "entityReferences"]
              }
            }
          ]
        }
      ],
      "toolConfig": {
        "functionCallingConfig": {
          "mode": "ANY"
        }
      },
      "generationConfig": {
        "temperature": 0.3,
        "maxOutputTokens": 128
      }
  }'