Mariabackup: Why does to_lsn not change in an incremental backup?

Hello,

I'm trying to create an incremental backup with mariabackup for a script. While it works, there's one thing I don't understand. In the documentation, it is stated that the first full backup should contain the following in xtrabackup_checkpoints:

backup_type = full-backuped  
from_lsn = 0  
to_lsn = 1635102  
last_lsn = 1635102  
recover_binlog_info = 0 

The first incremental backup should have:

backup_type = full-backuped  
from_lsn = 0  
to_lsn = 1635102  
last_lsn = 1635102  
recover_binlog_info = 0 

We can see that the from_lsn of the incremental backup matches the to_lsn and last_lsn of the full backup. However, when I test it on my side, I get a different result. For the full backup:

backup_type = full-backuped  
from_lsn = 0  
to_lsn = 46830  
last_lsn = 6306692

And for the incremental backup:

backup_type = incremental  
from_lsn = 46830  
to_lsn = 46830  
last_lsn = 6891089 

The from_lsn of the incremental backup seems correct, but the to_lsn hasn't changed. However, even the last_lsn has increased (I'm adding data between the dumps). When I look in the target-dir, I can see the new data.

I also tested with the latest version, but apart from xtrabackup_checkpoints being renamed to mariadb_backup_checkpoints, I get the same result.

How does it work? Thank.