[Koha] Newly imported users all get booked the enrollment fee

[Michael Kuhn]

I had an empty Koha database with a user type "Adults" where enrollment 
period is set to 12 months, enrollment fee set to 10 Euro. Using menu 
"Tools > Import patrons" I loaded a number of users with user type 
"Adults" into the database, which went OK. Only the next day when the 
script "fines.pl" had run I saw that all these users had a fee of 10 
Euro booked on their account. It seems like Koha thought all these users 
were newly enrolled so it booked the fee.

All these users were migrated from another system and had already paid 
their fees, so there is no reason to book these 10 Euro. How can I 
prevent this behaviour?

Or, if I can't prevent it - will it be enough to delete the respective 
lines in Koha table "accountlines"?

I did not find much information about how the process of enrolling and 
the booking of the fee works. Basing on what date will the next fee get 
due etc.

I appreciate any help!

Kind regards, Michael