When setting courses -> backups - old generation are not deleted

I was setting the courses->backups I set every Sunday in 2:00 O'Clock and keep= 2 ( 2 generations) in a folder that I set too,

but actually it keep saving more than 2 , in fact it saves endless every Sunday and not deleting the old generations. now I have 10 generation and my disk is almost full.

Why doesn't it delete the old zip course generation?
The Moodle Debugger doesn't say anything,

Thanks for the help