double activation emails at new user registrations

dear team,
i am running a combination of wordpress+buddypress+pro sites plugin, everything on the latest version, hosted on wp engine

a few days ago i noticed that new registered users receive two activation emails, one comes with activation url

http://sitename.com/aktivieren/?key=1507d42c8c0fdc7e (which comes from buddypress i assume)

and the other activation url is
http://sitename.com/wp-activate.php?key=1507d42c8c0fdc7e

as you can see, both send the same key. using the first, registration/activation ist fine, the user is able to login with it´s username/password from registration.
using the second, the user is being activated, but receives an additional email with a NEW password, like as the system should generate a password for the user.

i tried to find out which setting in my configuration or plugin causes that issue and noticed that when i deactivate the "pro sites" plugin, everything is fine, users only receive one activation email, which comes from buddypress.

can you please have a look into this, in my sites it´s a serious problem.

tnx, eric