The reason your diskstation may stop sleeping after this update is due to the 'winbindd' service continually touching a file (/usr/syno/etc/private/winbind_domain_list) which is hosted on disk. The continual touching of the file results in the disks being unable to sleep.
An issue which this update fixed is related to this service, so I suspect it was unintentionally introduced to fix a separate issue (specifically regarding RW access of Guest users).
To get your diskstation sleeping again, you simply have to stop the winbindd service. You can do this via the simple command "stop winbindd" via command line. Note that disabling that service will likely reintroduce the Guest RW issue which was fixed in this update.
Note that this service will automatically restart when your diskstation reboots. The permanent fix will need to come from Synology.
As a side note, you can use the following command line to hunt for any files modified within the last 30 minutes on your diskstation. This is what I used to find the above issue:
find / -path /dev -prune -o -path /proc -prune -o -path /run -prune -o -path /tmp -prune -o -mmin -30 -print
(The 'prune' flags will exclude paths which aren't hosted off of disk, such as /proc and /run)