to keep everything clean I think it's very good that I can only install in a empty database. Also if you enter wrong database connection information, this is very good -> so you cannot override an existing database by a fault.
Shouldn't be so heavy to give c5 a stand-alone database. Maybe switch your hosting company?
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I have verified this bug still exists in the current version of concrete5.
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http://php5.c5host.com/