If someone edits a debit type, the DB description is deleted, replaced by NULL. I've only tried it with the RENT* debit types, as those were the ones reported to me. I suspect it would do the same for all system types, but haven't tested.

1. In the database, get the list of debit types

select * from account_debit_types;

--> They should all have a description

2. Go to Administration > Debit types
3. Click "Show all debit types"
4. Click "Edit" next to RENT
5. Check "Can be manually invoiced?"
6. Click "Save"
7. Click "Show all debit types"
--> Notice the description for RENT is still visible
8. Redo the query in the database
--> The description for RENT is now NULL
9. Optionally, go to Reports > Cash register (under Statistics wizards)
10. Open the dropdown of transaction types
--> There is an empty space where the RENT description should be