Create documents with long strings inside them. Try to retrieve documents using get or multi-get. See that single callbacks or spooled callbacks do not always get called.
Error is demonstrated best when creating documents with strings of greater than 1200 characters, with the error occurring more often the larger the strings.
See following gist for test case:
Case should insert 4 documents with strings of 5000 characters each, then attempt to retrieve them 50 times. Will hang if error occurs.