DataMapper ORM v1.8.2

[eluser]WanWizard[/eluser]
I can not reproduce it here, if I set a prefix in an existing model it immediately complains it can't find the table, and gives the table name with the prefix.

Which leads me to believe that you're not using the latest version of the code.

So the same advice as to @Ikkes: Please download the latest version (https://bitbucket.org/wanwizard/datamapper/get/tip.zip) and upgrade your installation.