In Greek, intervocalic -pw-, -bw-, -bhw - probably resulted in -ππ-, -ββ-, -πφ-, though these may have occured by the side of -π-, -β-, -φ-, at least locally. Such examples as νή-πιος, ύπερ-φίαλος (Brugmann, Gr. I 2 311 f.) represent the initial not the medial development and are therefore not here in point, since the w would here regularly disappear. This is true also of Lat. amā-bam, -bo, super-bus. This difference in treatment is due to the fact that in the true medial position the syllabic division was between the labial and w. In Latin, medial pw, bw, fw, mw undergo progressive assimilation : pv to pp; bv, bb ; fa, ff; mv mm. The geminations thus arising are regularly simplified when the accent follows. Hence aperto, operio for *apperio, *opperio, Umbr. subocauu from *subbocāyō.
A Wed, study studied this question.