Yes it can. Test it yourself: 1) Create a new user/database for a 1 mysql plan client website. 2) Enter phpmyadmin and create a second database! for web1_u1 created in ispconfig you can create a second database called web1?u1 (strange stuff) Maybe this is a phpmyadmin issue (?)
Thats a bug in older mysql versions. MySQL never solved it in the 4.0 and 4.1 series. It is solved in MySQL 5 if i remember correctly.