That is the default behavior of PPP. You can configure 'no peer neighbor-route' to prevent the /32 from being installed:
http://www.cisco.com/warp/public/104/dcprob.html#5a
http://www.cisco.com/univercd/cc/td/doc/product/software/ios112/112cg_cr/4rbook/4rppp.htm#xtocid289148