An odd observation about 1st pl. *-men-, 2nd pl. *-ten- that
everybody leaves out of the discussion: Sanskrit uses for reflexive
pronouns the words 'atmán' "soul" and 'tanú' "body" (the latter so
named because it has 'extension', as opposed to the soul which
doesn't). I thought the similarity was too striking to be ignored.
note also that the fact that the stress pattern of these two persons
differ from that of the other persons entails that the nature of the
nexus in which the words that later fused into an inflected form had
entered, was different in the two cases.
http://www.angelfire.com/rant/tgpedersen/mn.html
http://www.angelfire.com/rant/tgpedersen/tn1.html
Torsten