I keep saying that they aren't human and things can easily be read wrong, like words that are spelled the same, and mean different things. ALso two words together can have a completely different meaning. The search only finds what we ask it to find...
But here's an interesting example, outside of Micro.
http://news.msn.com/pop-culture/confused-by-thatcher-tweets-cher-fans-upset-by-numbernowthatchersdeadTweet about Margret Thatchers Death
#nowthatchersdead (Now Thatchers Dead) sent some people into a panic because they read it as Now That Chers Dead (also noting most were American's)
hashtag double-entendres are like bad keyword searches, all the letters and words are there, it's just some unintended result with a different meaning.