I agree with your point also, regarding mishearing. Actually it's not even mishearing, it's the alternative pronunciation, as you mentioned. I have heard some pretty funny ones, and by native speakers as well; ranging from "..shmas!" to a bellowed "Yoooosu!" (clearly leaning towards our aforementioned ubiquitous "osu!").
Not to mention the tendency for some non-Japanese to pronounce the "gae" in onegaeshimasu as "gei" (Japanese pronunciation stated), creating a sentence that sounds llike something spoken by Yoda - have fum enterpreting what he might be saying:-)