Deceptively
People think it means:
Nobody is sure.
Actually means:
Nobody is sure.
Specifically, we're talking about when the word is used with some other adjective. Like if somebody says, "The [...] pool is deceptively shallow," does that mean it's deeper than it appears, or not as deep?
If you're not sure, don't feel bad. The American Heritage Dictionary asked their word experts and they said they had no fucking idea, either. So ... nobody knows.
[...]
If ever there was a case to be made for clarity of language, this is it. If you use it at all, make sure the context makes the meaning totally clear. "My balls are deceptively large," you could say, "because I have just inflated my genitalia with a bicycle pump."
What this also means is that technically the usage is never wrong ... or right...
From:
http://www.cracked.com/article_15664_9-words-that-dont-mean-what-you-think.html
Now, that strikes me as a less than authoritative source. Doesn't it mean, "In a deceptive fashion?" Where is the confusion?