Fixing (un)common Moodle errors

1. Site Administration block with unexpandable links

The problem: in the "Site administration" block, the links such as "users", "courses", "grades" (or any other links that must expand on a click) do not work like they're supposed to.
The context: I ran into this issue after I've changed the location of "moodledata" directory on the server (Ubuntu 12.04 LTS; Moodle 2.5.1).
The solution: I had to purge the caches via command line, as follows:

sudo su www-data -c "php admin/cli/purge_caches.php"

Here are some links that I found on this issue. However, I didn't find out the reason for this problem to appear:

• Administration block links not working on some browsers
• Sometimes site menu items don't open (expand) on mouse clic 

2. "Incorrect access detected, this server may be accessed only through..."

The problem: i have an instance of Moodle behind a proxy and the former (the instance) is mapped in the local proxy URL space by use of ProxyPass and ProxyPassReverse directives. I have modified the "$CFG->wwwroot" parameter from "config.php" to match the proxy server domain name, but I still get the error message:

Incorrect access detected, this server may be accessed only through "http://xxx.xxx.xxx.xxx/moodle" address, sorry.

The context: Ubuntu 14.04.02 LTS; Moodle 2.8.5+).
The solution: add to "config.php", before the "lib/setup.php" include directive,  the line:

$CFG->reverseproxy = true;