Yes some characters are forbidden for security reasons - some others can be bugged too ... I don't know why these characters were forbidden. Need to ask mose . It is delicate to change the security check
If you want you can change the list in :
$patterns['string'] = "/^[^\";#]*$/"; // find, and such extended chars $vartype['page'] = 'string';
Better to look in the code for the real list - another bug
These characters give back an "invalid varaible value"
Other ones can be bugged. It will be interesting to establish the list.