I ran into the following incorrect C code for this snippet of Vala:

public abstract class Folks.AbstractFieldDetails<T> : Object
{
  private T _value;
  public virtual T @value
    {
      get { return this._value; }
      set { this._value = value; }
    }
...
}

public class Folks.FieldDetails : AbstractFieldDetails<string>
{
  public FieldDetails (string value)
    {
      Object (value: value);
    }
...

================

Generated C:

FolksFieldDetails* folks_field_details_construct (GType object_type, const gchar* value) {
  FolksFieldDetails * self = NULL;
  g_return_val_if_fail (value != NULL, NULL);

  // XXX: note that G_TYPE_STRING through g_free should not be there, which causes this to segfault accessing 0x40 (G_TYPE_STRING) as a string
  self = (FolksFieldDetails*) g_object_new (object_type, G_TYPE_STRING, (GBoxedCopyFunc) g_strdup, g_free, "value", value, NULL);
  return self;
}