Incremental backup would auto-delete full version backup

[hiphiphip]

I setted a backup job to backup a folder about 3.4G, auto-delete was set to 30 days.
But it didn't do a full backup every 30 days, all files under /var/www/files are small than 60M.
There is no full version backup.
I don't know how restore works but 30*60M < 3.4G
I think it need to keep two full version backup to make it possible to restore to any given day within 30 days.

[PetaByet]

Could you provide the backup logs if you have them?

[hiphiphip]

I tried to reproduce this problem, need to wait a few days to know the results.
May be caused by my deletion.
After delete backups

                    foreach ($backups as $key => $backup) {
                        if ($backup['file'] == $_REQUEST['id']) {
                            unset($backups[$key]);
                        }
                    }
                    file_put_contents($config['path'] . '/db/db-backups.json', json_encode($backups));

This would turn

[{"id":"26dd99457553d087d4330a1a931ce694","file":"cdpme-2015-10-28-18-26-21-26dd99457553d087d4330a1a931ce694.tar.gz","size":29761524,"time":1446056781},{"id":"7c27e3a5d70f3f39793eb005deb1615b","file":"cdpme-2015-10-28-18-26-39-7c27e3a5d70f3f39793eb005deb1615b.tar.gz","size":123400,"time":1446056798}]

into

{"0":{"id":"26dd99457553d087d4330a1a931ce694","file":"cdpme-2015-10-28-18-26-21-26dd99457553d087d4330a1a931ce694.tar.gz","size":29761524,"time":1446056781}}

keys was added to jason files.
That's why some records are missing, and some reasons are not in order.
Add

$backups = array_values($backups);

before

file_put_contents($config['path'] . '/db/db-backups.json', json_encode($backups));

could solve this issue.
The same situation may also occur when dbbackupjob/acl/user was deleted.

Another two issues:

• Size of big backups is displayed as "NAN"
• IP in "Last 10 Activity Logs" shows right IP address, but IP in "Last 10 Backup Logs" shows "Not found"

[hiphiphip]

I setted a increamental backup keep for 3 days, still no full version archive.
There is nothing in particular in /var/log/syslog.
I could set a demo server for testing.