Index: src/wp-includes/class-wp-user.php
===================================================================
--- src/wp-includes/class-wp-user.php	(revision 42771)
+++ src/wp-includes/class-wp-user.php	(working copy)
@@ -486,7 +486,7 @@
 	 *
 	 * @return array List of all capabilities for the user.
 	 */
-	public function get_role_caps() {
+	 public function get_role_caps() {
 		$switch_site = false;
 		if ( is_multisite() && $this->site_id != get_current_blog_id() ) {
 			$switch_site = true;
@@ -494,27 +494,43 @@
 			switch_to_blog( $this->site_id );
 		}
 
-		$wp_roles = wp_roles();
+ 		$wp_roles = wp_roles();
 
-		// Filter out caps that are not role names and assign to $this->roles.
-		if ( is_array( $this->caps ) ) {
-			$this->roles = array_filter( array_keys( $this->caps ), array( $wp_roles, 'is_role' ) );
+ 		// Filter out caps that are not role names and assign to $this->roles.
+ 		if ( is_array( $this->caps ) ) {
+ 			$this->roles = array_filter( array_keys( $this->caps ), array( $wp_roles, 'is_role' ) );
 		}
 
-		// Build $allcaps from role caps, overlay user's $caps.
-		$this->allcaps = array();
-		foreach ( (array) $this->roles as $role ) {
-			$the_role      = $wp_roles->get_role( $role );
-			$this->allcaps = array_merge( (array) $this->allcaps, (array) $the_role->capabilities );
-		}
-		$this->allcaps = array_merge( (array) $this->allcaps, (array) $this->caps );
+ 		// Build $allcaps from role caps, overlay user's $caps.
+ 		$this->allcaps = array();
+ 		foreach ( (array) $this->roles as $role ) {
+ 			$the_role = $wp_roles->get_role( $role );
 
+ 			/*
+			 * Merge role capabilities.
+			 * Have to use this approach, instead of array_merge,
+			 * to make sure a "0" in one role doesn't overwrite a "1" on another.
+			 */
+ 			foreach( (array) $the_role->capabilities as $cap => $value ) {
+ 				if ( ! isset( $this->allcaps[ $cap ] ) || ( ! $this->allcaps[ $cap ] && $value ) ) {
+ 					$this->allcaps[ $cap ] = $value;
+ 				}
+ 			}
+ 		}
+
+ 		// Merge role capabilities.
+ 		foreach( (array) $this->caps as $cap => $value ) {
+ 			if ( ! isset( $this->allcaps[ $cap ] ) || ( ! $this->allcaps[ $cap ] && $value ) ) {
+ 				$this->allcaps[ $cap ] = $value;
+ 			}
+ 		}
+
 		if ( $switch_site ) {
 			restore_current_blog();
 		}
 
-		return $this->allcaps;
-	}
+ 		return $this->allcaps;
+ 	}
 
 	/**
 	 * Add role to user.