at least in the current 'production' version of sendmail (8.12.10) the sendmail binary is installed as /usr/sbin/sendmail while this location is also used by mailwrapper; this results in one package overwriting the other possible solution is to install the sendmail binary as /usr/sbin/sendmail.sendmail to follow the mailwrapper convention for naming MTAs
New version (See GWN) should take care of this problem (once the bugs get worked out).