Amount in XDR is negative. Why?

Question

I'm trying to submit a transaction that includes a payment operation. Sometimes the transaction succeeds. However, sometimes it fails. I believe this has something to do with the decimal being submitted.

Before submitting the transaction, the decimal prints as:

11.776242893769199616

On failed transactions, if I browse the XDR response (via Stellar laboratory), I see a negative amount:

amount: -6.6705011 (raw: -66705011)

Any idea why this is a negative number?

Response:

Post Payment Error: Horizon request error of type request failed with message: {
  "type": "https://stellar.org/horizon-errors/transaction_failed",
  "title": "Transaction Failed",
  "status": 400,
  "detail": "The transaction failed when submitted to the stellar network. The `extras.result_codes` field on this response contains further details.  Descriptions of each code can be found at: https://www.stellar.org/developers/learn/concepts/list-of-operations.html",
  "extras": {
    "envelope_xdr": "[XDR INFO]",
    "result_codes": {
      "transaction": "tx_failed",
      "operations": [
        "op_malformed"
      ]
    },
    "result_xdr": "AAAAAAAAAGT/////AAAAAQAAAAAAAAAB/////wAAAAA="
  }
}

Answer 1

When I pasted the decimal you posted into the stellar transaction builder I got the following error: "Amount can only support a precision of 7 decimals."

Perhaps whatever method it uses to encode decimals does not support that level of precision and fails spectacularly (underflow, overflow?).

https://www.stellar.org/laboratory/#txbuilder?params=eyJvcGVyYXRpb25zIjpbeyJpZCI6MCwiYXR0cmlidXRlcyI6eyJhbW91bnQiOiIxMS43NzYyNDI4OTM3NjkxOTk2MTYifSwibmFtZSI6InBheW1lbnQifV19&network=test