All 3 of my win8/win8.1 computers have the scheduled optimization ON (frequency: daily or weekly). I can manually trim the SSD by clicking on Optimize but when I checked after a few weeks, last run always showed the date of my last manual trim and current status showed "xx days since the last trim."
I have noticed the same and think its just buggy same as Win 8/8.1 as a whole. Run it once per week manually.
I want to report back what I find out: Trim not working automatically is caused by the default parameters in the scheduled windows defrag task (all versions of windows 8 including the spring update). The default parameters are -c -h -o -$. -$ is not documented anywhere but it has the same effect as "traditional defrag". -c is also problematic as it causes an 0x80070057 error, probably trying to defrag volumes other than c:. So the fix is to change the parameters to c: -h -o (and add additional drive letters appropriately). Note that after changing the default defrag parameters, you won't be able to access the Optimize window without reverting back all the default parameters. To do a manual trim, you'll have to run "defrag c: -h -o' in an elevated command prompt.