What kinds of out-of-band failures am I forgetting to test?

I came across an amazing presentation years ago (which of course I can't find) that listed a bunch of kinds of failures for remote services that people usually don't test for.

In addition to timeout, 4xx, 5xx, etc, it listed things like:

• connection closes after 10 bytes of data
• returns contents of www.google.com
• returns contents of /dev/random
• returns contents of /etc/passwd
• returns correctly-formatted unicode chinese text
• returns ansi color control characters
• returns an incorrect content-type, labeled correctly (You requested Content-Type: application/json, I send back Content-Type: application/jpeg)
• returns one byte of data every 29 seconds

What are some types of "out-of-band failures" you've encountered that developers don't usually (but should) test for?

(extra bonus points if you can find the original presentation)