My main site Self.my is using BuddyPress Social 1.3.1 on WP 3.3.1 version and BP 1.5.2. I enable the same BuddyPress Social 1.3.1 on my second site WebStory.my, under the same multisite WP install, and if I specify the Post Page setting under Settings->Reading->Front page displays: A static page->Post Page, it would redirect to Webstory.my's Home page.
This bug is confirmed when I switch back to BuddyPress Default 1.5.2 and it works properly.
Another bug is the menu, after assigning a page as the Front Page under Settings->Reading->Front page displays: A static page->Front Page, it will still show up as a menu item for BP Social 1.3.1 (older version i.e. 1.1.8 was ok), and BuddyPress Default 1.5.2 behaves correctly.