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 newRef = xref.getNewRef();
    const AP = new Dict(xref);
    AP.set("N", newRef);
    const encrypt = xref.encrypt;
    let originalTransform = null;
    let newTransform = null;
    if (encrypt) {
      originalTransform = encrypt.createCipherTransform(
        this.ref.num,
        this.ref.gen
      );
      newTransform = encrypt.createCipherTransform(newRef.num, newRef.gen);
      appearance = newTransform.encryptString(appearance);
    }
    dict.set("V", isAscii(value) ? value : stringToUTF16BEString(value));
    dict.set("AP", AP);
    dict.set("M", `D:${getModificationDate()}`);
    const appearanceDict = new Dict(xref);
    appearanceDict.set("Length", appearance.length);
    appearanceDict.set("Subtype", Name.get("Form"));
    appearanceDict.set("Resources", this._getSaveFieldResources(xref));
    appearanceDict.set("BBox", bbox);
    const bufferOriginal = [`${this.ref.num} ${this.ref.gen} obj\n`];
    writeDict(dict, bufferOriginal, originalTransform);
    bufferOriginal.push("\nendobj\n");
    const bufferNew = [`${newRef.num} ${newRef.gen} obj\n`];
    writeDict(appearanceDict, bufferNew, newTransform);
    bufferNew.push(" stream\n");
    bufferNew.push(appearance);
    bufferNew.push("\nendstream\nendobj\n");