Does urbackup adjust disk usage figures after a deletion?

I am setting up my first urbackup system.

The server is 4.9.0-8-amd64 #1 SMP Debian 4.9.130-2 (2018-10-27) x86_64 GNU/Linux and urbackup-server using a 5T ext4 disk.

I did a full file backup on a client after a few false starts and the deleted the previous backups using the web interface. I noticed that the reported backup size of the backup I kept did not increase and the statistics are under reporting the disk usage checked via du in the client backup directory.

Does the system recalculate usage at some time or can I cause an update somehow?

I assume all files are present in the last backup as the du shows 5.2G though the web statistics page shows 1.26G.