Is there any way we can work around this?
Our Joomla install was quite happy to use a db of format xxnn-yyyyyy.
When we create or rename db using phpMyAdmin we can only choose the yyyyyy. "xxnn-" is automatic.
The CiviCRM Installer had an error to the question "Is the provided database name valid? The database name provided is not valid. Please use only 0-9, a-z, A-Z and _ as characters in the name."