Attempting to reproduce issue couchbase/couchbase-lite-ios#63 ... no success so far.

ModelTests2.m

// Append this to ModelTests.m

TestCase(API_ModelAttachments) {
    // Attempting to reproduce https://github.com/couchbase/couchbase-lite-ios/issues/63
    CBLDatabase* db = createEmptyDB();
    NSError* error;

    NSData* attData = [@"Ceci n'est pas une pipe." dataUsingEncoding: NSUTF8StringEncoding];
    CBLDocument* doc;
    {
        TestModel* model = [[TestModel alloc] initWithNewDocumentInDatabase: db];
        doc = model.document;
        model.number = 1337;
        CAssert([model save: &error], @"Initial failed: %@", error);

        CBLAttachment* attachment = [[CBLAttachment alloc] initWithContentType: @"text/plain"
                                                                          body: attData];

        [model addAttachment: attachment named: @"Caption.txt"];
        CAssert([model save: &error], @"Save after adding attachment failed: %@", error);

        model.number = 23;
        CAssert([model save: &error], @"Save after updating number failed: %@", error);
    }
    {
        TestModel* model = [TestModel modelForDocument: doc];
        CAssertEq(model.number, 23);
        CBLAttachment* attachment = [model attachmentNamed: @"Caption.txt"];
        CAssertEqual(attachment.body, attData);

        model.number = -1;
        CAssert([model save: &error], @"Save of new model object failed: %@", error);

        // Now update the attachment:
        [model removeAttachmentNamed: @"caption.txt"];
        NSData* newAttData = [@"sluggo" dataUsingEncoding: NSUTF8StringEncoding];
        attachment = [[CBLAttachment alloc] initWithContentType: @"text/plain"
                                                                          body: newAttData];
        [model addAttachment: attachment named: @"Caption.txt"];
        CAssert([model save: &error], @"Final save failed: %@", error);
    }
}