CSSMin.inc max_execution_time 60 leaks outside to drush

I have a drupal site with advagg 7.x.2.17 on server A and on server B I have a cronjob where I do:

ssh SERVER_A_IP -p 22 drush -r /web-pub/site pm-disable readonlymode -y
ssh SERVER_A_IP -p 22 drush -r /web-pub/site pm-enable readonlymode -y

The enable of readonlymode takes more than 60 seconds and I get:

Fatal error: Maximum execution time of 60 seconds exceeded in /web-pub/site/sites/all/modules/contrib/features/features.export.inc on line 1090

Nowhere in my code I have set a limit of 60 seconds. In fact, I've set it to 6000 seconds.

I recursively grepped my whole site on server A using:

grep -r --include "*.php" --include "*.inc" "max_exe" /web-pub/site/ | grep 60

and I only got:

/web-pub/site/sites/all/modules/contrib/advagg/advagg_css_compress/yui/CSSMin.inc:        $this->max_execution_time = 60; // 1 min

I changed that 60 to 61. Next time my cron job on server B run I got the error:

Fatal error: Maximum execution time of 61 seconds exceeded in /web-pub/site/sites/all/modules/contrib/features/features.export.inc on line 0

So, it seems that the limit that is leaking outside of that module originates from advagg's CSSMin code.

I don't know why enabling a third party module (in this case readonlymode) initiates code in the advagg, but the fact that advagg doesn't honour the time limit I've explicitly set in my settings.php seems like a problem to me.