Lamer and hombre in Spanish

Why is it that Latin lambere became lamer (lick) and Latin homo became hombre (man) in Spanish? Why is it that when there was an mb, both bilabial consonants, the second consonant got lost in lambere, but an extra b (plus an r) was added in hombre (from Latin homo, hominis) and in hambre (from Latin famis, famis)? There seem to be two divergent phenomena here.