Well, this is really not supported at all by Class::DBI and is very likely to cause you problems all over the place. I would advise you to make separate classes. However, I can tell you how to fix this specific problem.

Class::DBI keeps track of which objects you have in memory. See the "UNIQUENESS OF OBJECTS IN MEMORY" section of the docs for an explanation. You can either turn off this feature, or just remove the object from memory before trying to fetch it again. Here's an example:

my $foo = FooBar->retrieve(1);
print $foo->name(), "\n";
# remove the instance of FooBar with an ID of 1 from memory
undef $foo;

FooBar->table('Bar'); #switch table
my $bar1 = FooBar->retrieve(1);
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