I am using CCleaner within another application (std or 64 bit has the same error) and the "completed OK" status is returned on loading rather than on completion.
Command line "C:\Program Files\CCleaner\CCleaner.exe" /auto
I have been using CCleaner with SyncBackFree for several years in the run before mode where CCleaner cleans out temp files and caches before backing up the User files, however recently I noticed that the backup had started before CCleaner had finished. I didn't notice how many udates ago this happened.
Using their "test" button CCleaner gives an OK response as the program loads, it used to wait until the program closed. I selected both CCleaner versions to check if was a recent upgrade of mine to Win8.1 64bit that was responsible. It has the same problem on my Windows 7 setups.
It is always possible that SyncBack has changed and is asking for the loaded rather than the completion status, so I am going to mention this problem on their forum aswell.
UPDATE: This bug reported on the SyncBack forum. Workaround tip is to put the program in a batch file and run that. The suggester indicated that another program worked OK. but not CCleaner.
I have tried the workaround, but CCleaner is running so fast after several runs that I cannot tell for sure now - It will wait until later to be sure.