As a child, I was precociously good at spelling. So much so that at age ten, I was pointed towards the Oxford English Dictionary and told to pick my own spellings to learn each week. No one taught me IPA, however, which meant that although I could spell Madagascar, chlorofluorocarbon and other similarly lengthy and/or difficult words, I never found out how to pronounce them. I was fifteen before I found out that Madagascar isn't pronounced ['mah-duh-guh-''saah-kuh] and that [in-dikt-munt] is usually pronounced [in-dite-munt]. Even now, from time to time, I will say a word I've seen in writing but never heard in speech before and will be me with stares and then laughter.
Most recently, though, I've been a victim of orthographical hypercorrection. On the radio, I've often heard people mentioning [mef-uh-drone] and as many people in southern England pronounce th as f, I assumed this drug was spelled methedrone. I was hypercorrecting, of course, and am clearly a massive snob for assuming that everyone else is just labialising their dental fricative (th is pronounced by pushing air past the tip of the tongue against the teeth; f involves blowing air past the teeth against the lower lip).
On the other hand, mephedrone has been in the news a lot recently. Both methadone and methedrone are also drugs and I have potentially heard them mentioned on the news in the past. I have definitely been hypercorrecting recently but this error may have been reinforced by having heard the other two words in the past.
