Link to PDF file (or attach file here): [detect-form-fields.pdf](https://github.com/mozilla/pdf.js/files/287227/detect-form-fields.pdf)

Configuration:
- Web browser and its version: Firefox 46.0.1
- Operating system and its version: Ubuntu 16.04
- PDF.js version: 1.3.231
- Is an extension: No

Steps to reproduce the problem:
1. Open PDF
2. Look at entered text in form sections 8a and 9a

What is the expected behavior? Text is correct size:

![screenshot from 2016-05-27 12-32-04](https://cloud.githubusercontent.com/assets/33672/15619145/32ff065a-2407-11e6-8cfb-95905526fd91.png)

What went wrong? Text is very large:

![screenshot from 2016-05-27 12-30-58](https://cloud.githubusercontent.com/assets/33672/15619160/45016442-2407-11e6-85c0-faee9879c20d.png)

PdfBug console output:

```
11:56:13.291 PDF ef2293a3b9f4e0accbef97ee38798a2c [1.3 Mac OS X 10.11.1 Quartz PDFContext / Amgraf OneForm Designer Plus] (PDF.js: 1.3.231)1 viewer.js:6800:7
11:56:13.292 Warning: AcroForm/XFA is not supported1 viewer.js:6824:9
11:56:13.424 Warning: Unimplemented annotation type "FreeText", falling back to base annotation1 pdf.worker.js:9407:5
11:56:13.806 Warning: fontRes not available1 pdf.worker.js:9407:5 (logged 54 times)
11:56:13.898 Warning: Error during font loading: Font Helvetica-Bold is not available1 pdf.js:368:5
```

const defaultValue = this.data.fieldValue && this.data.fieldValue !== "Off";
    if (defaultValue === value) {
      return null;
    }
    const dict = evaluator.xref.fetchIfRef(this.ref);
    if (!isDict(dict)) {
      return null;
    }
    const xfa = {
      path: stringToPDFString(dict.get("T") || ""),
      value: value ? this.data.exportValue : "",
    };
    const name = Name.get(value ? this.data.exportValue : "Off");
    dict.set("V", name);
    dict.set("AS", name);
    dict.set("M", `D:${getModificationDate()}`);
    const encrypt = evaluator.xref.encrypt;
    let originalTransform = null;
    if (encrypt) {
      originalTransform = encrypt.createCipherTransform(
        this.ref.num,
        this.ref.gen
      );
    }
    const buffer = [`${this.ref.num} ${this.ref.gen} obj\n`];
    writeDict(dict, buffer, originalTransform);
    buffer.push("\nendobj\n");
    return [{ ref: this.ref, data: buffer.join(""), xfa }];
  }
  async _saveRadioButton(evaluator, task, annotationStorage) {