GetManifestResourceStream stopped working in Xamarin Studio 5.9.0?

I just took the latest downloads:

• Mono Framework MDK 4.0.0.143
• Xamarin Studio 5.9.0
• Xamarin.Android 5.1.0.115
• Xamaring.iOS 8.10.0.267

I have this code, which was working previously:
private void LoadGemsFromFile(string resource)
{
index = -1;
Assembly assembly = this.GetType ().GetTypeInfo ().Assembly;

                    // TODO:  Need to read in a device agnostic fashion
                // http://developer.xamarin.com/guides/cross-platform/xamarin-forms/working-with/files/
                using (Stream stream = assembly.GetManifestResourceStream(resource)) {
                    using (StreamReader reader = new StreamReader (stream)) {
                        string line;
                        while ((line = reader.ReadLine ()) != null) {
                            index++;
                            string[] items = line.Split (DELIMITER, 2, StringSplitOptions.None);
                            if (items.Length > 0) {
                                GemRecord record = new GemRecord ();
                                record.Message = items [0].Trim (TRIM_CHARS);
                                if (items.Length > 1) {
                                    record.Author = items [1].Trim (TRIM_CHARS);
                                }
                                record.GemIndex = index;
                                theList.Add (record);
                            }
                        }
                    }
                }
            }

where resource = "HelloForms.GemPack1.txt"

This used to work but now assembly.GetManifestResourceStream returns null.

"HelloForms" is a PCL which references GemsModel, which is a shared project.

In GemsModel, the structure is:
GemsModel
GemPacks
GemPack1.txt

I double checked that Build Action is still EmbeddedResource for GemPack1.txt.

Can anyone tell me what is going wrong and how to fix it?