Index: bp-activity/bp-activity-functions.php
===================================================================
--- bp-activity/bp-activity-functions.php
+++ bp-activity/bp-activity-functions.php
@@ -48,11 +48,7 @@ function bp_activity_find_mentions( $content ) {
 
 	// We've found some mentions! Check to see if users exist
 	foreach( (array) $usernames as $key => $username ) {
-		if ( bp_is_username_compatibility_mode() ) {
-			$user_id = username_exists( $username );
-		} else {
-			$user_id = bp_core_get_userid_from_nicename( $username );
-		}
+		$user_id = bp_core_get_userid_from_nicename( $username );
 
 		// user ID exists, so let's add it to our array
 		if ( ! empty( $user_id ) ) {
Index: bp-members/bp-members-functions.php
===================================================================
--- bp-members/bp-members-functions.php
+++ bp-members/bp-members-functions.php
@@ -271,10 +271,6 @@ function bp_core_get_username( $user_id, $user_nicename = false, $user_login = f
 		$update_cache = false;
 	}
 
-	// Check $username for empty spaces and default to nicename if found
-	if ( strstr( $username, ' ' ) )
-		$username = bp_members_get_user_nicename( $user_id );
-
 	// Add this to cache
 	if ( ( true == $update_cache ) && !empty( $username ) )
 		wp_cache_set( 'bp_user_username_' . $user_id, $username, 'bp' );
@@ -848,21 +844,6 @@ function bp_core_ucfirst( $str ) {
 }
 
 /**
- * Strips spaces from usernames that are created using add_user() and wp_insert_user()
- *
- * @package BuddyPress Core
- */
-function bp_core_strip_username_spaces( $username ) {
-	// Don't alter the user_login of existing users, as it causes user_nicename problems.
-	// See http://trac.buddypress.org/ticket/2642
-	if ( username_exists( $username ) && ( !bp_is_username_compatibility_mode() ) )
-		return $username;
-
-	return str_replace( ' ', '-', $username );
-}
-add_action( 'pre_user_login', 'bp_core_strip_username_spaces' );
-
-/**
  * When a user logs in, check if they have been marked as a spammer. If yes then simply
  * redirect them to the home page and stop them from logging in.
  *
Index: bp-members/bp-members-template.php
===================================================================
--- bp-members/bp-members-template.php
+++ bp-members/bp-members-template.php
@@ -950,6 +950,21 @@ function bp_displayed_user_username() {
 		return apply_filters( 'bp_get_displayed_user_username', $username );
 	}
 
+function bp_displayed_user_nicename() {
+	echo bp_get_displayed_user_nicename();
+}
+	function bp_get_displayed_user_nicename() {
+		global $bp;
+
+		if ( bp_displayed_user_id() ) {
+			$username = $bp->displayed_user->userdata->user_nicename;
+		} else {
+			$username = '';
+		}
+
+		return apply_filters( 'bp_get_displayed_user_nicename', $username );
+	}
+
 function bp_loggedin_user_username() {
 	echo bp_get_loggedin_user_username();
 }
@@ -965,6 +980,21 @@ function bp_loggedin_user_username() {
 		return apply_filters( 'bp_get_loggedin_user_username', $username );
 	}
 
+function bp_loggedin_user_nicename() {
+	echo bp_get_loggedin_user_nicename();
+}
+	function bp_get_loggedin_user_nicename() {
+		global $bp;
+
+		if ( bp_loggedin_user_id() ) {
+			$username = $bp->loggedin_user->userdata->user_nicename;
+		} else {
+			$username = '';
+		}
+
+		return apply_filters( 'bp_get_loggedin_user_nicename', $username );
+	}
+
 /** Signup Form ***************************************************************/
 
 /**
Index: bp-templates/bp-legacy/buddypress/members/single/member-header.php
===================================================================
--- bp-templates/bp-legacy/buddypress/members/single/member-header.php
+++ bp-templates/bp-legacy/buddypress/members/single/member-header.php
@@ -21,7 +21,7 @@
 
 <div id="item-header-content">
 
-	<h2 class="user-nicename">@<?php bp_displayed_user_username(); ?></h2>
+	<h2 class="user-nicename">@<?php bp_displayed_user_nicename(); ?></h2>
 	<span class="activity"><?php bp_last_activity( bp_displayed_user_id() ); ?></span>
 
 	<?php do_action( 'bp_before_member_header_meta' ); ?>
Index: bp-themes/bp-default/members/single/member-header.php
===================================================================
--- bp-themes/bp-default/members/single/member-header.php
+++ bp-themes/bp-default/members/single/member-header.php
@@ -25,7 +25,7 @@
 		<a href="<?php bp_displayed_user_link(); ?>"><?php bp_displayed_user_fullname(); ?></a>
 	</h2>
 
-	<span class="user-nicename">@<?php bp_displayed_user_username(); ?></span>
+	<span class="user-nicename">@<?php bp_displayed_user_nicename(); ?></span>
 	<span class="activity"><?php bp_last_activity( bp_displayed_user_id() ); ?></span>
 
 	<?php do_action( 'bp_before_member_header_meta' ); ?>