profile picture you upload on buddpress is not used

it's probably related but maybe a more common problem that you already have dealt with in the past:
I have a buddpress setup on one subsite and I am using "Multi-Domains for Multisite" so you only need to log in once. Basic problem: Buddypress on one subsite and the Blog on the main subsite currently. But the profile picture you upload on Buddypress is not used as profile photo on the blog site.