[TYPO3-mvc] Extending Tx_Extbase_Domain_Model_FrontendUser

[Rens Admiraal]

In our model we have a Person object which extends 
Tx_Extbase_Domain_Model_FrontendUser, the goal is to save the record also in 
the fe_users table, but somehow we can't get it working.

We have the following typoscript in ext_typoscript_setup.txt:
config.tx_<LC_ext> {
	persistence {
		enableAutomaticCacheClearing = 1
		updateReferenceIndex = 0
		classes {
			Tx_<CC_ext>_Domain_Model_Person {
				mapping {
					tableName = fe_users
					columns {
						usergroup.foreignClass = Tx_Extbase_Domain_Model_FrontendUserGroup
						lockToDomain.mapOnProperty = lockToDomain
					}
				}
			}
		}
	}
}

This should be ok somehow, because it's a copy of the typoscript in extbase 
;-)
The problem is that after submitting a registration form I get the error:
Table 'tx_<LC_ext>_domain_model_person' doesn't exist

Why doesn't the table map to the fe_users table?