I have been having problem with HTML editor buttons disappearing on my Moodle site.
I have many Moodle installations on my site.
Moodle installations on addon domains have this problem.
Moodle installations on the main domain work fine.
After days of invistigation I found the problem relies in .htaccess file.
If I delete this file the problem is solved!!
Any idea how to solve this problem without the trade off for security by deleting .htaccess file?