Christmas 2010, I gifted my friend, a big fan of Penny Arcade, the first episode of the Penny Arcade game. Two episodes were out, but I figured I'd just give him the first, and leave it up to him whether he liked it enough to get the second one.
Fastforward to today, when the Penny Arcade game came up in conversation, and he mentions he never played it and that I randomly gifted him only the second episode. Confused, I checked my email receipt, and my transaction history within Steam itself, and both say I bought and gifted the first episode, but it's definitely not on his account, and instead he has the second one. (Edit: to be clear, each episode is a separate application, and they aren't all lumped together like TellTale's The Walking Dead or anything).
I'm not sure it's worth contacting Steam support for, especially when I only spent $5, and my friend said he'll probably just buy the first episode during the next big Steam sale now that he remembered he has it. But still, that's really weird, and I'm curious to hear if anybody else has had anything like that happen.