I have been conviced for a long time that both 人前{にんまえ} and 人前{ひとまえ} existed. Which is backed by this wikitionary page.
Recently, I just wanted to warn another Japanese learner about this pair of tricky words. By any chance, at this time, a native speaker was with us. Some minutes later she asked me where I heard にんまえ. I did not remember so I could not answer well. (According to the meaning of にんまえ I should have seen it in a recipe or something of this kind).
Nevertheless, the fact that she was a bit troubled by にんまえ made me investigate a bit. The result of my investigation is that neither 明鏡辞書 nor goo nor 大辞林 have any record about にんまえ but all of them reference ひとまえ.
This leads me to wonder whether にんまえ really exists as a word. And if so, what does it really mean and what is its usage?
Edit: It seems that 一人前{いちにんまえ} exists and mean 一人分{ひとりぶん}