Forehead, in OED fo red. In Webster's Collegiate (American), also for ed.
(I can't do the phonetic symbols, so have approximated).
The 'h' is skipped over in both, although in the 12th c., spelling suggests the 'h' was pronounced, but unfortunately, we have no aural recordings from that time.

Often is just an alteration of oft, but in the OED often is given the prounciation, of 'n.
In this case, the OED lists a possible culprit for "of ten"- Singers. "Often used in singing." They also say that of ten is "now frequent in the south of England."
Webster's Collegiate also gives o fen; no of ten.
In other words literate people ignore the 't.'

Interesting to a trivialist like me. Hmmm, I think I will coin the term triviologist to add stature to this important study.