I have tried running CCleaner as Admin, as the "User", and as user "run as administrator" -- but the Explorer thumbnail cache files remain. I am tempted to delete these myself, but there are also a couple of other system files in that folder with "etl" extensions that I don't know the purpose of, and would rather not mess with it unless I fully understood the consequences.
it shouldn't automagically restart explorer, ending the process should keep it closed till its manually restarted. To my knowledge though, those files shouldn't be deleted and the Thumbcachetodelete (or something) should be.
Those huge thumb cache files are the result of the <user> exploring a large database of photos (1677 to be exact) earlier TODAY. I believe I have the CCleaner settings to ignore temp files newer than 24 hours -- Doh!